Method for purification of as-produced single-wall carbon nanotubes

ABSTRACT

This invention relates generally to a single-wall carbon nanotube (SWNT) purification process and more particularly to a purification process that comprises heating the SWNT-containing felt under oxidizing conditions to remove the amorphous carbon deposits and other contaminating materials. In a preferred mode of this purification procedure, the felt is heated in an aqueous solution of an inorganic oxidant, such as nitric acid, a mixture of hydrogen peroxide and sulfuric acid, or a potassium permanganate. Preferably, SWNT-containing felts are refluxed in an aqueous solution of an oxidizing acid at a concentration high enough to etch away amorphous carbon deposits within a practical time frame, but not so high that the single-wall carbon nanotube material will be etched to a significant degree. When material having a high proportion of SWNT is purified, the preparation produced will be enriched in single-wall nanotubes, so that the SWNT are substantially free of other material.

RELATED APPLICATIONS

This application is a division of prior U.S. patent application Ser. No.09/380,545, filed on Dec. 22, 1999, now U.S. Pat. No. 6,683,783,entitled “CARBON FIBERS FORMED FROM SINGLE-WALL CARBON NANOTUBES,” whichis the 35 U.S.C. § 371 national application of International ApplicationNumber PCT/US98/04513 filed on Mar. 6, 1998, which designated the UnitedStates, claiming priority to: provisional U.S. patent application Ser.No. 60/067,325, filed on Dec. 5, 1997; provisional U.S. patentapplication Ser. No. 60/064,531, filed on Nov. 5, 1997; provisional U.S.patent application Ser. No. 60/063,675, filed on Oct. 29, 1997;provisional U.S. patent application Ser. No. 60/055,037, filed on Aug.8, 1997; provisional U.S. patent application Ser. No. 60/047,854, filedon May 29, 1997; and provisional U.S. patent application Ser. No.60/040,152, filed on Mar. 7, 1997. Each of the foregoing applications iscommonly assigned to the assignee of the present invention and is herebyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Fullerenes are closed-cage molecules composed entirely of sp²-hybridizedcarbons, arranged in hexagons and pentagons. Fullerenes (e.g., C₆₀) werefirst identified as closed spheroidal cages produced by condensationfrom vaporized carbon.

Fullerene tubes are produced in carbon deposits on the cathode in carbonare methods of producing spheroidal fullerenes from vaporized carbon.Ebbesen et al. (Ebbesen I), “Large-Scale Synthesis Of Carbon Nanotubes,”Nature, Vol. 358, p. 220 (Jul. 16, 1992) and Ebbesen et al., (EbbesenII). “Carbon Nanotubes,” Annual Review of Materials Science, Vol. 24, p.235 (1994). Such tubes are referred to herein as carbon nanotubes. Manyof the carbon nanotubes made by these processes were multi-wallnanotubes, i.e., the carbon nanotubes resembled concentric cylinders.Carbon nanotubes having up to seven walls have been described in theprior art. Ebbesen II; Iijima et al., “Helical Microtubules Of GraphiticCarbon,” Nature, Vol. 354, p. 56 (Nov. 7, 1991).

Single-wall carbon nanotubes have been made in a DC arc dischargeapparatus of the type used in fullerene production by simultaneouslyevaporating carbon and a small percentage of Group VIII transition metalfrom the anode of the arc discharge apparatus. See Iijima et al.,“Single-Shell Carbon Nanotubes of 1 nm Diameter,” Nature, Vol. 363, p.603 (1993); Bethune et al., “Cobalt Catalyzed Growth of Carbon Nanotubeswith Single Atomic Layer Walls,” Nature, Vol. 63, p. 605 (1993); Ajayanet al., “Growth Morphologies During Cobalt Catalyzed Single-Shell CarbonNanotube Synthesis,” Chem. Phys. Lett., Vol. 215, p. 509 (1993); Zhou etal., “Single-Walled Carbon Nanotubes Growing Radially From YC₂Particles,” Appl. Phys. Lett., Vol. 65, p. 1593 (1994); Seraphin et al.,“Single-Walled Tubes and Encapsulation of Nanocrystals Into CarbonClusters,” Electrochem. Soc., Vol. 142, p. 290 (1995); Saito et al.,“Carbon Nanocapsules Encaging Metals and Carbides,” J. Phys. Chem.Solids, Vol. 54, p. 1849 (1993); Saito et al., “Extrusion of Single-WallCarbon Nanotubes Via Formation of Small Particles Condensed Near anEvaporation Source,” Chem. Phys. Lett., Vol. 236, p. 419 (1995). It isalso known that the use of mixtures of such transition metals cansignificantly enhance the yield of single-wall carbon nanotubes in thearc discharge apparatus. See Lambert et al., “Improving ConditionsToward Isolating Single-Shell Carbon Nanotubes,” Chem. Phys. Lett., Vol.226, p. 364 (1994).

While this arc discharge process can produce single-wall nanotubes, theyield of nanotubes is low and the tubes exhibit significant variationsin structure and size between individual tubes in the mixture.Individual carbon nanotubes are difficult to separate from the otherreaction products and purify.

An improved method of producing single-wall nanotubes is described inU.S. Ser. No. 08/687,655, entitled “Ropes of Single-Walled CarbonNanotubes” incorporated herein by reference in its entirely. This methoduses, inter alia, laser vaporization of a graphite substrate doped withtransition metal atoms, preferably nickel, cobalt, or a mixture thereof,to produce single-wall carbon nanotubes in yields of at least 50% of thecondensed carbon. The single-wall nanotubes produced by this method tendto be formed in clusters, termed “ropes,” of 10 to 1000 single-wallcarbon nanotubes in parallel alignment, held together by van der Waalsforces in a closely packed triangular lattice. Nanotubes produced bythis method vary in structure, although one structure tends topredominate.

Although the laser vaporization process produces improved single-wallnanotube preparations, the product is still heterogeneous, and thenanotubes are too tangled for many potential uses of these materials. Inaddition, the vaporization of carbon is a high energy process and isinherently costly. Therefore, there remains a need for improved methodsof producing single-wall nanotubes of greater purity and homogeneity.Furthermore, many practical materials could make use of the propertiesof single-wall carbon nanotubes if only they were available asmacroscopic components. However, such components have not been producedup to now.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a high yield,single step method for producing large quantities of continuousmacroscopic carbon fiber from single-wall carbon nanotubes usinginexpensive carbon feedstocks at moderate temperatures.

It is another object of this invention to provide macroscopic carbonfiber made by such a method.

It is also an object of this invention to provide a molecular array ofpurified single-wall carbon nanotubes for use as a template incontinuous growing of macroscopic carbon fiber.

It is another object of the present invention to provide a method forpurifying single-wall carbon nanotubes from the amorphous carbon andother reaction products formed in methods for producing single-wallcarbon nanotubes (e.g., by carbon vaporization).

It is also an object of the present invention to provide a new class oftubular carbon molecules, optionally derivatized with one or morefunctional groups, which are substantially free of amorphous carbon.

It is also an object of this invention to provide a number of devicesemploying the carbon fibers, nanotube molecular arrays and tubularcarbon molecules of this invention.

It is an object of this invention to provide composite materialcontaining carbon nanotubes.

It is another object of this invention to provide a composite materialthat is resistant to delamination.

A method for purifying a mixture comprising single-wall carbon nanotubesand amorphous carbon contaminate is disclosed. The method includes thesteps of heating the mixture under oxidizing conditions sufficient toremove the amorphous carbon, followed by recovering a product comprisingat least about 80% by weight of single-wall carbon nanotubes.

In another embodiment, a method for producing tubular carbon moleculesof about 5 to 500 nm in length is also disclosed. The method includesthe steps of cutting single-wall nanotube containing-material to form amixture of tubular carbon molecules having lengths in the range of 5-500nm and isolating a fraction of the molecules having substantially equallengths. The nanotubes disclosed may be used, singularly or inmultiples, in power transmission cables, in solar cells, in batteries,as antennas, as molecular electronics, as probes and manipulators, andin composites.

In another embodiment, a method for forming a macroscopic moleculararray of tubular carbon molecules is disclosed. This method includes thesteps of providing at least about 10⁶ tubular carbon molecules ofsubstantially similar length in the range of 50 to 500 nm; introducing alining moiety onto at least one end of the tubular carbon molecules;providing a substrate coated with a material to which the linking moietywill attach; and contacting the tubular carbon molecules containing alinking moiety with the substrate.

In another embodiment, another method for forming a macroscopicmolecular array of tubular carbon molecules is disclosed. First, ananoscale array of microwells is provided on a substrate. Next, a metalcatalyst is deposited in each microwells. Next, a stream of hydrocarbonor CO feedstock gas is directed at the substrate under conditions thateffect growth of single-wall carbon nanotubes from each microwell.

In another embodiment, still another method for forming a macroscopicmolecular array of tubular carbon molecules is disclosed. It includesthe steps of providing surface containing purified but entangled andrelatively endless single-wall carbon nanotube material; subjecting thesurface to oxidizing conditions sufficient to cause short lengths ofbroken nanotubes to protrude up from the surface; and applying anelectric field to the surface to cause the nanotubes protruding from thesurface to align in an orientation generally perpendicular to thesurface and coalesce into an array by van der Waals interaction forces.

In another embodiment, a method for continuously growing a macroscopiccarbon fiber comprising at least about 10⁶ single-wall nanotubes ingenerally parallel orientation is disclosed. In this method, amacroscopic molecular array of at least about 10⁶ tubular carbonmolecules in generally parallel orientation and having substantiallysimilar lengths in the range of from about 50 to about 500 nanometers isprovided. The hemispheric fullerene cap is removed from the upper endsof the tubular carbon molecules in the array. The upper ends of thetubular carbon molecules in the array are then contacted with acatalytic metal. A gaseous source of carbon is supplied to the end ofthe array while localized energy is applied to the end of the array inorder to heat the end to a temperature in the range of about 500° C. toabout 1300° C. The growing carbon fiber is continuously recovered.

In another embodiment, a macroscopic molecular array comprising at leastabout 10⁶ single-wall carbon nanotubes in generally parallel orientationand having substantially similar lengths in the range of from about 5 toabout 500 nanometers is disclosed.

In another embodiment, a composition of matter comprising at least about80% by weight of single-wall carbon nanotubes is disclosed.

In still another embodiment, macroscopic carbon fiber comprising atleast about 10⁶ single-wall carbon nanotubes in generally parallelorientation is disclosed.

In another embodiment, an apparatus for forming a continuous macroscopiccarbon fiber from a macroscopic molecular template array comprising atleast about 10⁶ single-wall carbon nanotubes having a catalytic metaldeposited on the open ends of said nanotubes is disclosed. Thisapparatus includes a means for locally heating only the open ends of thenanotubes in the template array in a growth and annealing zone to atemperature in the range of about 500° C. to about 1300° C. It alsoincludes a means for applying a carbon-containing feedstock gas to thegrowth and annealing zone immediately adjacent the heated open ends ofthe nanotubes in the template array. It also includes a means forcontinuously removing growing carbon fiber from the growth and annealingzone while maintaining the growing open end of the fiber in the growthand annealing zone.

In another embodiment, a composite material containing nanotubes isdisclosed. This composite material includes a matrix and a carbonnanotube material embedded within said matrix.

In another embodiment, a method of producing a composite materialcontaining carbon nanotube material is disclosed. It includes the stepsof preparing an assembly of a fibrous material; adding the carbonnanotube material to the fibrous material; and adding a matrix materialprecursor to the carbon nanotube material and the fibrous material.

In another embodiment, a three-dimensional structure of derivatizedsingle-wall nanotube molecules that spontaneously form is disclosed. Itincludes several component molecule having multiple derivatives broughttogether to assemble into the three-dimensional structure.

The foregoing objectives, and others apparent to those skilled in theart, are achieved according to the present invention as described andclaimed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an apparatus for practicing the invention.

FIG. 2 is a diagram of an apparatus for practicing the inventionutilizing two different laser pulses to vaporize the composite rodtarget.

FIG. 3A is a TEM spectrum of purified SWNTs according to the presentinvention.

FIG. 3B is a SEM spectrum of purified SWNTs according to the presentinvention.

FIG. 3C is a Raman spectrum of purified SWNTs according to the presentinvention.

FIG. 4 is a schematic representation of a portion of an homogeneous SWNTmolecular array according to the present invention.

FIG. 5 is a schematic representation of an heterogeneous SWNT moleculararray according to the present invention.

FIG. 6 is a schematic representation of the growth chamber of the fiberapparatus according to the present invention.

FIG. 7 is a schematic representation of the pressure equalization andcollection zone of the fiber apparatus according to the presentinvention.

FIG. 8 is a composite array according to the present invention.

FIG. 9 is a composite array according to the present invention.

FIG. 10 is a power transmission cable according to the presentinvention.

FIG. 11 is a schematic representation of a bistable, nonvolatilenanoscale memory device according to the present invention.

FIG. 12 is a graph showing the energy wells that correspond to each ofthe bistable states in the memory bit of FIG. 11.

FIG. 13 is a schematic representation of a lithium ion secondary batteryaccording to the present invention.

FIG. 14 is an anode for a lithium ion battery according to the presentinvention.

FIG. 15A is a medium-magnification transmission electron microscopeimage of single-wall nanotubes.

FIG. 15B is a high-magnification image of adjacent single-wall carbonnanotubes.

FIG. 15C is a high-magnification image of adjacent single-wall carbonnanotubes.

FIG. 15D is a high-magnification image of adjacent single-wall carbonnanotubes.

FIG. 15E is a high-magnification image of the cross-section of sevenadjacent single-wall carbon nanotubes.

FIG. 16A is a scanning electron microscope (SEM) image of rawsingle-walled fullerene nanotube felt.

FIG. 16B is a SEM image of the single-wall fullerene nanotube feltmaterial of FIG. 16A after purification.

FIG. 16C is a SEM image of the single-walled fullerene nanotube feltafter tearing, resulting in substantial alignment of the single-wallednanotube rope fibers.

FIG. 17 is an atomic force microscopy image of cut fullerene nanotubesdeposited on highly oriented pyrolytic graphite.

FIG. 18A is a graph of field flow fractionation (FFF) of a cut nanotubessuspension.

FIGS. 18B, 18C, and 18D represent the distribution of fullerenenanotubes lengths measured by AFM on three collections.

FIG. 19 shows an AFM image of a fullerene nanotube “pipe” tethered totwo 10 nm gold spheres.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Carbon has from its very essence not only the propensity toself-assemble from a high temperature vapor to form perfect spheroidalclosed cages (of which C₆₀ is prototypical), but also (with the aid of atransition metal catalyst) to assemble into perfect single-wallcylindrical tubes which may be sealed perfectly at both ends with asemifullerene dome. These tubes, which may be thought of asone-dimensional single crystals of carbon, are true fullerene moleculeshaving no dangling bonds.

Single-wall carbon nanotubes of this invention are much more likely tobe free of defects than multi-wall carbon nanotubes. Defects insingle-wall carbon nanotubes are less likely than defects inmulti-walled carbon nanotubes because the latter can survive occasionaldefects, while the former have no neighboring walls to compensate fordefects by forming bridges between unsaturated carbon valences. Sincesingle-wall carbon nanotubes will have fewer defects, they are stronger,more conductive, and therefore more useful than multi-wall carbonnanotubes of similar diameter.

Carbon nanotubes, and in particular the single-wall carbon nanotubes ofthis invention, are useful for making electrical connectors in microdevices such as integrated circuits or in semiconductor chips used incomputers because of the electrical conductivity and small size of thecarbon nanotube. The carbon nanotubes are useful as antennas at opticalfrequencies, and as probes for scanning probe microscopy such as areused in scanning tunneling microscopes (STM) and atomic forcemicroscopes (AFM). The carbon nanotubes may be used in place of or inconjunction with carbon black in tires for motor vehicles. The carbonnanotubes are also useful as supports for catalysts used in industrialand chemical processes such as hydrogenation, reforming and crackingcatalysts.

Ropes of single-wall carbon nanotubes made by this invention aremetallic, i.e., they will conduct electrical charges with a relativelylow resistance. Ropes are useful in any application where an electricalconductor is needed, for example as an additive in electricallyconductive paints or in polymer coatings or as the probing tip of anSTM.

In defining carbon nanotubes, it is helpful to use a recognized systemof nomenclature. In this application, the carbon nanotube nomenclaturedescribed by M. S. Dresselhaus, G. Dresselhaus, and P. C. Eklund,Science of Fullerness and Carbon Nanotubes, Chap. 19, especially pp.756-760, (1996), published by Academic Press, 525 B Street, Suite 1900,San Diego, Calif. 92101-4495 or 6277 Sea Harbor Drive, Orlando, Fla.32877 (ISBN 0-12-221820-5), which is hereby incorporated by reference,will be used. The single wall tubular fullerenes are distinguished fromeach other by double index (n,m) where n and m are integers thatdescribe how to cut a single strip of hexagonal “chicken-wire” graphiteso that it makes the tube perfectly when it is wrapped onto the surfaceof a cylinder and the edges are sealed together. When the two indicesare the same, m=n, the resultant tube is said to be of the “arm-chair”(or n,n) type, since when the tube is cut perpendicular to the tubeaxis, only the sides of the hexagons are exposed and their patternaround the periphery of the tube edge resembles the arm and seat of anarm chair repeated n times. Arm-chain tubes are a preferred form of asingle-wall carbon nanotubes since they are metallic, and have extremelyhigh electrical and thermal conductivity. In addition, all single-wallnanotubes have extremely high tensile strength.

The dual laser pulse feature described herein produces an abundance of(10,10) single-wall carbon nanotubes. The (10,10), single-wall carbonnanotubes have an approximate tube diameter of 13.8 Å±0.3 Å or 13.8Å±0.2 Å.

The present invention provides a method for making single-wall carbonnanotubes in which a laser beam vaporizes material from a targetcomprising, consisting essentially of, or consisting of a mixture ofcarbon and one or more Group VI or Group VIII transition metals. Thevapor from the target forms carbon nanotubes that are predominantlysingle-wall carbon nanotubes, and of those, the (10, 10) tube ispredominant. The method also produces significant amounts of single-wallcarbon nanotubes that are arranged as ropes, i.e., the single-wallcarbon nanotubes run parallel to each other. Again, the (10, 10) tube isthe predominant tube found in each rope. The laser vaporization methodprovides several advantages over the arc discharge method of makingcarbon nanotubes: laser vaporization allows much greater control overthe conditions favoring growth of single-wall carbon nanotubes, thelaser vaporization method permits continuous operation, and the laservaporization method produces single-wall carbon nanotubes in higheryield and of better quality. As described herein, the laser vaporizationmethod may also be used to produce longer carbon nanotubes and longerropes.

Carbon nanotubes may have diameters ranging from about 0.6 nanometers(nm) for a single-wall carbon nanotube up to 3 nm, 5 nm, 10 nm, 30 nm,60 nm or 100 nm for single-wall or multi-wall carbon nanotubes. Thecarbon nanotubes may range in length from 50 nm up to 1 millimeter (mm),1 centimeter (cm), 3 cm, 5 cm, or greater. The yield of single-wallcarbon nanotubes in the product made by this invention is unusuallyhigh. Yields of single-wall carbon nanotubes greater than 10 wt %,greater than 30 wt % and greater than 50 wt % of the material vaporizedare possible with this invention.

As will be described further, the one or more Group VI or VIIItransition metals catalyze the growth in length of a carbon nanotubeand/or the ropes. The one or more Group VI or VIII transition metalsalso selectively produce single-wall carbon nanotubes and ropes ofsingle-wall carbon nanotubes in high yield. The mechanism by which thegrowth in the carbon nanotube and/or rope is accomplished is notcompletely understood. However, it appears that the presence of the oneor more Group VI or VIII transition metals on the end of the carbonnanotube facilitates the addition of carbon from the carbon vapor to thesolid structure that forms the carbon nanotube. Applicants believe thismechanism is responsible for the high yield and selectivity ofsingle-wall carbon nanotubes and/or ropes in the product and willdescribe the invention utilizing this mechanism as merely an explanationof the results of the invention. Even if the mechanism is provedpartially or wholly incorrect, the invention which achieves theseresults is still fully described herein.

One aspect of the invention comprises a method of making carbonnanotubes and/or ropes of carbon nanotubes which comprises supplyingcarbon vapor to the live end of a carbon nanotube while maintaining thelive end of a carbon nanotube in an annealing zone. Carbon can bevaporized in accordance with this invention by an apparatus in which alaser beam impinges on a target comprising carbon that is maintained ina heated zone. A similar apparatus has been described in the literature,for example, in U.S. Pat. No. 5,300,203 which is incorporated herein byreference, and in Chai, et al., “Fullerenes with Metals Inside,” J.Phys. Chem., vol. 95, no. 20, p. 7564 (1991).

Carbon nanotubes having at least one live end are formed when the targetalso comprises a Group VI or VIII transition metal or mixtures of two ormore Group VI or VIII transition metals. In this application, the term“live end” of a carbon nanotube refers to the end of the carbon nanotubeon which atoms of the one or more Group VI or VIII transition metals arelocated. One or both ends of the nanotube may be a live end. A carbonnanotube having a live end is initially produced in the laservaporization apparatus of this invention by using a laser beam tovaporize material from a target comprising carbon and one or more GroupVI or VIII transition metals and then introducing the carbon/Group VI orVIII transition metal vapor to an annealing zone. Optionally, a secondlaser beam is used to assist in vaporizing carbon from the target. Acarbon nanotube having a live end will form in the annealing zone andthen grow in length by the catalytic addition of carbon from the vaporto the live end of the carbon nanotube. Additional carbon vapor is thensupplied to the live end of a carbon nanotube to increase the length ofthe carbon nanotube.

The carbon nanotube that is formed is not always a single-wall carbonnanotube; it may be a multi-wall carbon nanotube having two, five, tenor any greater number of walls (concentric carbon nanotubes).Preferably, though, the carbon nanotube is a single-wall carbon nanotubeand this invention provides a way of selectively producing (10, 10)single-wall carbon nanotubes in greater and sometimes far greaterabundance than multi-wall carbon nanotubes.

The annealing zone where the live end of the carbon nanotube isinitially formed should be maintained at a temperature of 500° to 1500°C., more preferably 1000° to 1400° C. and most preferably 1100 to 1300°C. In embodiments of this invention where carbon nanotubes having liveends are caught and maintained in an annealing zone and grown in lengthby further addition of carbon (without the necessity of adding furtherGroup VI or VIII transition metal vapor), the annealing zone may becooler, 400° to 1500° C., preferably 400° to 1200° C., most preferably500° to 700° C. The pressure in the annealing zone should be maintainedin the range of 50 to 2000 Torr., more preferably 100 to 800 Torr. andmost preferably 300 to 600 Torr. The atmosphere in the annealing zonewill comprise carbon. Normally, the atmosphere in the annealing zonewill also comprise a gas that sweeps the carbon vapor through theannealing zone to a collection zone. Any gas that does not prevent theformation of carbon nanotubes will work as the sweep gas, but preferablythe sweep gas is an inert gas such as helium, neon, argon, krypton,xenon, radon, or mixtures of two or more of these. Helium and Argon aremost preferred. The use of a flowing inert gas provides the ability tocontrol temperature, and more importantly, provides the ability totransport carbon to the live end of the carbon nanotube. In someembodiments of the invention, when other materials are being vaporizedalong with carbon, for example one or more Group VI or VIII transitionmetals, those compounds and vapors of those compounds will also bepresent in the atmosphere of the annealing zone. If a pure metal isused, the resulting vapor will comprise the metal. If a metal oxide isused, the resulting vapor will comprise the metal and ions or moleculesof oxygen.

It is important to avoid the presence of too many materials that kill orsignificantly decrease the catalytic activity of the one or more GroupVI or VIII transition metals at the live end of the carbon nanotube. Itis known that the presence of too much water (H₂O) and/or oxygen (O₂)will kill or significantly decrease the catalytic activity of the one ormore Group VI or VIII transition metals. Therefore, water and oxygen arepreferably excluded from the atmosphere in the annealing zone.Ordinarily, the use of a sweep gas having less than 5 wt %, morepreferably less than 1 wt % water and oxygen will be sufficient. Mostpreferably the water and oxygen will be less than 0.1 wt %.

Preferably, the formation of the carbon nanotube having a live end andthe subsequent addition of carbon vapor to the carbon nanotube are allaccomplished in the same apparatus. Preferably, the apparatus comprisesa laser that is aimed at a target comprising carbon and one or moreGroup VI or VIII transition metals, and the target and the annealingzone are maintained at the appropriate temperature, for example bymaintaining the annealing zone in an oven. A laser beam may be aimed toimpinge on a target comprising carbon and one or more Group VI or VIIItransition metals where the target is mounted inside a quartz tube thatis in turn maintained within a furnace maintained at the appropriatetemperature. As noted above, the oven temperature is most preferablywithin the range of 1100° to 1300° C. The tube need not necessarily be aquartz tube; it may be made from any material that can withstand thetemperatures (1000° to 1500° C.). Alumina or tungsten could be used tomake the tube in addition to quartz.

Improved results are obtained where a second laser is also aimed at thetarget and both lasers are timed to deliver pulses of laser energy atseparate times. For example, the first laser may deliver a pulse intenseenough to vaporize material from the surface of the target. Typically,the pulse from the first laser will last about 10 nanoseconds (ns).After the first pulse has stopped, a pulse from a second laser hits thetarget or the carbon vapor or plasma created by the first pulse toprovide more uniform and continued vaporization of material from thesurface of the target. The second laser pulse may be the same intensityas the first pulse, or less intense, but the pulse from the second laseris typically more intense than the pulse from the first laser, andtypically delayed about 20 to 60 ns, more preferably 40 to 55 ns, afterthe end of the first pulse.

Examples of a typical specification for the first and second lasers aregiven in Examples 1 and 3, respectively. As a rough guide, the firstlaser may vary in wavelength from 11 to 0.1 micrometers, in energy from0.05 to 1 Joule and in repetition frequency from 0.01 to 1000 Hertz(Hz). The duration of the first laser pulse may vary from 10⁻¹³ to 10⁻⁶seconds (s). The second laser may vary in wavelength from 11 to 0.1micrometers, in energy from 0.05 to 1 Joule and in repetition frequencyfrom 0.01 to 1000 Hertz. The duration of the second laser pulse may varyfrom 10⁻¹³ s to 10⁻⁶ s. The beginning of the second laser pulse shouldbe separated from end of the first laser pulse by about 10 to 100 ns. Ifthe laser supplying the second pulse is an ultraviolet (UV) laser (anExcimer laser for example), the time delay can be longer, up to 1 to 10milliseconds. But if the second pulse is from a visible or infrared (IR)laser, then the adsorption is preferably into the electrons in theplasma created by the first pulse. In this case, the optimum time delaybetween pulses is about 20 to 60 ns, more preferably 40 to 55 ns andmost preferably 40 to 50 ns. These ranges on the first and second lasersare for beams focused to a spot on the target composite rod of about 0.3to 10 mm diameter. The time delay between the first and second laserpulses is accomplished by computer control that is known in the art ofutilizing pulsed lasers. Applicants have used a CAMAC crate from LeCroyResearch Systems, 700 Chestnut Ridge Road, Chestnut Ridge, N.Y.10977-6499 along with a timing pulse generator from Kinetics SystemsCorporation, 11 Maryknoll Drive, Lockport, Ill. 60441 and a nanopulserfrom LeCroy Research Systems. Multiple first lasers and multiple secondlasers may be needed for scale up to larger targets or more powerfullasers may be used. The main feature of multiple lasers is that thefirst laser should evenly ablate material from the target surface into avapor or plasma and the second laser should deposit enough energy intothe ablated material in the vapor or plasma plume made by the firstpulse to insure that the material is vaporized into atoms or smallmolecules (less than ten carbon atoms per molecule). If the second laserpulse arrives too soon after the first pulse, the plasma created by thefirst pulse may be so dense that the second laser pulse is reflected bythe plasma. If the second laser pulse arrives too late after the firstpulse, the plasma and/or ablated material created by the first laserpulse will strike the surface of the target. But if the second laserpulse is timed to arrive just after the plasma and/or ablated materialhas been formed, as described herein, then the plasma and/or ablatedmaterial will absorb energy from the second laser pulse. Also, it shouldbe noted that the sequence of a first laser pulse followed by a secondlaser pulse will be repeated at the same repetition frequency as thefirst and second laser pulses, i.e., 0.01 to 1000 Hz.

In addition to lasers described in the Examples, other examples oflasers useful in this invention include an XeF (365 nm wavelength)laser, an XeCl (308 nm wavelength) laser, a KrF (248 nm wavelength)laser or an ArF (193 nm wavelength) laser.

Optionally, but preferably, a sweep gas is introduced to the tubeupstream of the target and flows past the target carrying vapor from thetarget downstream. The quartz tube should be maintained at conditions sothat the carbon vapor and the one or more Group VI or VIII transitionmetals will form carbon nanotubes at a point downstream of the carbontarget but still within the heated portion of the quartz tube.Collection of the carbon nanotubes that form in the annealing zone maybe facilitated by maintaining a cooled collector in the internal portionof the far downstream end of the quartz tube. For example, carbonnanotubes may be collected on a water cooled metal structure mounted inthe center of the quartz tube. The carbon nanotubes will collect wherethe conditions are appropriate, preferably on the water cooledcollector.

Any Group VI or VIII transition metal may be used as the one or moreGroup VI or VIII transition metals in this invention. Group VItransition metals are chromium (Cr), molybdenum (Mo), and tungsten (W).Group VIII transition metals are iron (Fe), cobalt (Co), nickel (Ni),ruthenium (Ru), rhodium (Ph), palladium (Pd), osmium (Os), Iridium (Ir)and platinum (Pt). Preferably, the one or more Group VIII transitionmetals are selected from the group consisting of iron, cobalt,ruthenium, nickel and platinum. Most preferably, mixtures of cobalt andnickel or mixtures of cobalt and platinum are used. The one or moreGroup VI or VIII transition metals useful in this invention may be usedas pure metal, oxides of metals, carbides of metals, nitrate salts ofmetals, or other compounds containing the Group VI or VIII transitionmetal. Preferably, the one or more Group VI or VIII transition metalsare used as pure metals, oxides of metals, or nitrate salts of metals.The amount of the one or more Group VI or VIII transition metals thatshould be combined with carbon to facilitate production of carbonnanotubes having a live end, is from 0.1 to 10 atom per cent, morepreferably 0.5 to 5 atoms per cent and most preferably 0.5 to 1.5 atomper cent. In this application, atom per cent means the percentage ofspecified atoms in relation to the total number of atoms present. Forexample, a 1 atom % mixture of nickel and carbon means that of the totalnumber of atoms of nickel plus carbon, 1% are nickel (and the other 99%are carbon). When mixtures of two or more Group VI or VIII transitionmetals are used, each metal should be 1 to 99 atom % of the metal mix,preferably 10 to 90 atom % of the metal mix and most preferably 20 to 80atom % of the metal mix. When two Group VI or VIII transition metals areused, each metal is most preferably 30 to 70 atom % of the metal mix.When the Group VI or VIII transition metals are used, each metal is mostpreferably 20 to 40 atom % of the metal mix.

The one or more Group VI or VIII transition metals should be combinedwith carbon to form a target for vaporization by a laser as describedherein. The remainder of the target should be carbon and may includecarbon in the graphitic form, carbon in the fullerene form, carbon inthe diamond form, or carbon in compound form such as polymers orhydrocarbons, or mixtures of two or more of these. Most preferably, thecarbon used to make the target is graphite.

Carbon is mixed with the one or more Group VI or VIII transition metalsin the ratios specified and then, in the laser vaporization method,combined to form a target that comprises the carbon and the one or moreGroup VI or VIII transition metals. The target may be made by uniformlymixing carbon and the one or more Group VI or VIII transition metalswith carbon cement at room temperature and then placing the mixture in amold. The mixture in the mold is then compressed and heated to about130° C. for about 4 or 5 hours while the epoxy resin of the carboncement cures. The compression pressure used should be sufficient tocompress the mixture of graphite, one or more Group VI or VIIItransition metals and carbon cement into a molded form that does nothave voids so that the molded form will maintain structural integrity.The molded form is then carbonized by slowly heating it to a temperatureof 810° C. for about 8 hours under an atmosphere of flowing argon. Themolded and carbonized targets are then heated to about 1200° C. underflowing argon for about 12 hours prior to their use as a target togenerate a vapor comprising carbon and the one or more Group VI or VIIItransition metals.

The invention may be further understood by reference to FIG. 1 which isa cross-section view of laser vaporization in an oven. A target 10 ispositioned within tube 12. The target 10 will comprise carbon and maycomprise one or more Group VI or VIII transition metals. Tube 12 ispositioned in oven 14 which comprises insulation 16 and heating elementzone 18. Corresponding portions of oven 14 are represented by insulation16′ and heating element zone 18′. Tube 12 is positioned in oven 14 sothat target 10 is within heating element zone 18.

FIG. 1 also shows water cooled collector 20 mounted inside tube 12 atthe downstream end 24 of tube 12. An inert gas such as argon or heliummay be introduced to the upstream end 22 of tube 12 so that flow is fromthe upstream end 22 of tube 12 to the downstream end 24. A laser beam 26is produced by a laser (not shown) focused on target 10. In operation,oven 14 is heated to the desired temperature, preferably 1100° to 1300°C., usually about 1200° C. Argon is introduced to the upstream end 22 asa sweep gas. The argon may optionally be preheated to a desiredtemperature, which should be about the same as the temperature of oven14. Laser beam 26 strikes target 10 vaporizing material in target 10.Vapor from target 10 is carried toward the downstream end 24 by theflowing argon stream. If the target is comprised solely of carbon, thevapor formed will be a carbon vapor. If one or more Group VI or VIIItransition metals are included as part of the target, the vapor willcomprise carbon and one or more Group VI or VIII transition metals.

The heat from the oven and the flowing argon maintain a certain zonewithin the inside of the tube as an annealing zone. The volume withintube 12 in the section marked 28 in FIG. 1 is the annealing zone whereincarbon vapor begins to condense and then actually condenses to formcarbon nanotubes. The water cooled collector 20 may be maintained at atemperature of 700° C. or lower, preferably 500° C. or lower on thesurface to collect carbon nanotubes that were formed in the annealingzone.

In one embodiment of the invention, carbon nanotubes having a live endcan be caught or mounted on a tungsten wire in the annealing zoneportion of tube 12. In this embodiment, it is not necessary to continueto produce a vapor having one or more Group VI or VIII transitionmetals. In this case, target 10 may be switched to a target thatcomprises carbon but not any Group VI or VIII transition metal, andcarbon will be added to the live end of the carbon nanotube.

In another embodiment of the invention, when the target comprises one ormore Group VI or VIII transition metals, the vapor formed by laser beam26 will comprise carbon and the one or more Group VI or VIII transitionmetals. That vapor will form carbon nanotubes in the annealing zone thatwill then be deposited on water cooled collector 20, preferably at tip30 of water cooled collector 20. The presence of one or more Group VI orVIII transition metals in the vapor along with carbon in the vaporpreferentially forms carbon nanotubes instead of fullerenes. althoughsome fullerenes and graphite will usually be formed as well. In theannealing zone, carbon from the vapor is selectively added to the liveend of the carbon nanotubes due to the catalytic effect of the one ormore Group VI or VIII transition metals present at the live end of thecarbon nanotubes.

FIG. 2 shows an optional embodiment of the invention that can be used tomake longer carbon nanotubes wherein a tungsten wire 32 is stretchedacross the diameter of tube 12 downstream of target 10 but still withinthe annealing zone. After laser beam pulses hit the target 10 forming acarbon/Group VI or VIII transition metal vapor, carbon nanotubes havinglive ends will form in the vapor. Some of those carbon nanotubes will becaught on the tungsten wire and the live end will be aimed toward thedownstream end 24 of tube 12. Additional carbon vapor will make thecarbon nanotube grow. Carbon nanotubes as long as the annealing zone ofthe apparatus can be made in this embodiment. In this embodiment, it ispossible to switch to an all carbon target after initial formation ofthe carbon nanotubes having a live end, because the vapor need onlycontain carbon at that point.

FIG. 2 also shows part of second laser beam 34 as it impacts on target10. In practice, laser beam 26 and second laser beam 34 would be aimedat the same surface of target 10, but they would impact that surface atdifferent times as described herein.

It is also possible to stop the laser or lasers altogether. Once thesingle-wall carbon nanotube having a live end is formed, the live endwill catalyze growth of the single-wall carbon nanotube at lowertemperatures and with other carbon sources. The carbon source can beswitched to fullerenes, that can be transported to the live end by theflowing sweep gas. The carbon source can be graphite particles carriedto the live end by the sweep gas. The carbon source can be a hydrocarbonthat is carried to the live end by a sweep gas or a hydrogen gas ormixture of hydrocarbon gasses introduced to tube 12 to flow past thelive end. Hydrocarbons useful include methane, ethane, propane, butane,ethylene, propylene, benzene, toluene or any other paraffinic, olefinic,cyclic or aromatic hydrocarbon or any other hydrocarbon.

The annealing zone temperature in this embodiment can be lower than theannealing zone temperatures necessary to initially form the single-wallcarbon nanotube having a live end. Annealing zone temperatures can be inthe range of 400° to 1500° C., preferably 400 to 1200° C., mostpreferably 500° to 700° C. The lower temperatures are workable becausethe Group VI or VIII transition metal(s) catalyze the addition of carbonto the nanotube at these lower temperatures.

Measurements shows that the single-wall carbon nanotubes in the ropeshave a diameter of 13.8 Å±0.2 Å. A (10, 10) single-wall carbon nanotubehas a calculated diameter of about 13.6 Å, and the measurements on thesingle-wall carbon nanotubes in the ropes proves they are predominantlythe (10, 10) tube. The number of single-wall carbon nanotubes in eachrope may vary from about 5 to 5000, preferably about 10 to 1000, or 50to 1000, and most preferably about 100 to 500. The diameters of theropes range from about 20 to 200 Å, more preferably about 50 to 200 Å.The (10, 10) single-wall carbon nanotube predominates the tubes in theropes made by this invention. Ropes having greater than 10%, greaterthan 30%, greater than 50%, greater than 75%, and even greater than 90%(10, 10) single-wall carbon nanotubes have been produced. Ropes havinggreater than 50% greater than 75% and greater than 90% armchair (n, n)single-wall carbon nanotubes are also made by and are a part of thisinvention. The single-wall carbon nanotubes in each rope are arranged toform a rope having a 2-D triangular lattice having a lattice constant ofabout 17 Å. Ropes of 0.1 up to 10, 100 or 1,000 microns in length aremade by the invention. The resistivity of a rope made in accordance withthis invention was measured to be 0.34 to 1.0 micro ohms per meter at27° C. proving that the ropes are metallic.

A “felt” of the ropes described above may also be produced. The productmaterial is collected as a tangled collection of ropes stuck together ina mat referred to herein as a “felt.” The felt material collected fromthe inventive process has enough strength to withstand handling, and ithas been measured to be electrically conductive. Felts of 10 mm², 100mm², 1000 mm² or greater, are formed in the inventive process.

One advantage of the single-wall carbon nanotubes produced with thelaser vaporization in an oven method is their cleanliness. Typicaldischarge arc-produced single-wall carbon nanotubes are covered with athick layer of amorphous carbon, perhaps limiting their usefulnesscompared to the clean bundles of single-wall carbon nanotubes producedby the laser vaporization method. Other advantages and features of theinvention are apparent from the disclosure. The invention may also beunderstood by reference to Guo et al., “Catalytic Growth OfSingle-Walled Nanotubes By Laser Vaporization,” Chem. Phys. Lett., Vol.243, pp. 49-54 (1995).

The advantages achieved by the dual pulsed lasers insure that the carbonand metal go through the optimum annealing conditions. The dual laserpulse process achieves this by using time to separate the ablation fromthe further and full vaporization of the ablated material. These sameoptimum conditions can be achieved by using solar energy to vaporizecarbon and metals as described in U.S. application Ser. No. 08/483,045filed Jun. 7, 1995 which is incorporated herein by reference. Combiningany of the Group VI or VIII transition metals in place of the metalsdisclosed in the Ser. No. 08/483,045 application will produce thesingle-wall carbon nanotubes and the ropes of this invention.

Purification of Single-Wall Nanotubes

Carbon nanotubes in material obtained according to any of the foregoingmethods may be purified according to the methods of this invention. Amixture containing at least a portion of single-wall nanotubes (“SWNT”)may be prepared, for example, as described by Iijima, et al, or Bethune,et al. However, production methods which produce single-wall nanotubesin relatively high yield are preferred. In particular, laser productionmethods such as those disclosed in U.S. Ser. No. 08/687,665, may produceup to 70% or more single-wall nanotubes, and the single-wall nanotubesare predominately of the arm-chair structure.

The product of a typical process for making mixtures containingsingle-wall carbon nanotubes is a tangled felt which can includedeposits of amorphous carbon, graphite, metal compounds (e.g., oxides),spherical fullerenes, catalyst particles (often coated with carbon orfullerenes) and possibly multi-wall carbon nanotubes. The single-wallcarbon nanotubes may be aggregated in “ropes” or bundles of essentiallyparallel nanotubes.

When material having a high proportion of single-wall nanotubes ispurified as described herein, the preparation produced will be enrichedin single-wall nanotubes, so that the single-wall nanotubes aresubstantially free of other material. In particular, single-wallnanotubes will make up at least 80% of the preparation, preferably atleast 90%, more preferably at least 95% and most preferably over 99% ofthe material in the purified preparation.

The purification process of the present invention comprises heating theSWNT-containing felt under oxidizing conditions to remove the amorphouscarbon deposits and other contaminating materials. In a preferred modeof this purification procedure, the felt is heated in an aqueoussolution of an inorganic oxidant, such as nitric acid, a mixture ofhydrogen peroxide and sulfuric acid, or potassium permanganate.Preferably, SWNT-containing felts are refluxed in an aqueous solution ofan oxidizing acid at a concentration high enough to etch away amorphouscarbon deposits within a practical time frame, but not so high that thesingle-wall carbon nanotube material will be etched to a significantdegree. Nitric acid at concentrations from 2.0 to 2.6 M have been foundto be suitable. At atmospheric pressure, the reflux temperatures of suchan aqueous acid solution is about 120° C.

In a preferred process, the nanotube-containing felts can be refluxed ina nitric acid solution at a concentration of 2.6 M for 24 hours.Purified nanotubes may be recovered from the oxidizing acid byfiltration through, e.g., a 5 micron pore size TEFLON filter, likeMillipore Type LS. Preferably, a second 24 hour period of refluxing in afresh nitric solution of the same concentration is employed followed byfiltration as described above.

Refluxing under acidic oxidizing conditions may result in theesterification of some of the nanotubes, or nanotube contaminants. Thecontaminating ester material may be removed by saponification, forexample, by using a saturated sodium hydroxide solution in ethanol atroom temperature for 12 hours. Other conditions suitable forsaponification of any ester linked polymers produced in the oxidizingacid treatment will be readily apparent to those skilled in the art.Typically the nanotube preparation will be neutralized after thesaponification step. Refluxing the nanotubes in 6M aqueous hydrochloricacid for 12 hours has been found to be suitable for neutralization,although other suitable conditions will be apparent to the skilledartisan.

After oxidation, and optionally saponification and neutralization, thepurified nanotubes may be collected by settling or filtration preferablyin the form of a thin mat of purified fibers made of ropes or bundles ofSWNTs, referred to hereinafter as “bucky paper.” In a typical example,filtration of the purified and neutralized nanotubes on a TEFLONmembrane with 5 micron pore size produced a black mat of purifiednanotubes about 100 microns thick. The nanotubes in the bucky paper maybe of varying lengths and may consists of individual nanotubes, orbundles or ropes of up to 10³ single-wall nanotubes, or mixtures ofindividual single-wall nanotubes and ropes of various thicknesses.Alternatively, bucky paper may be made up of nanotubes which arehomogeneous in length or diameter and/or molecular structure due tofractionation as described hereinafter.

The purified nanotubes or bucky paper are finally dried, for example, bybaking at 850° C. in a hydrogen gas atmosphere, to produce dry, purifiednanotube preparations.

When laser-produced single-wall nanotube material, produced by thetwo-laser method of U.S. Ser. No. 08/687,665, was subjected refluxing in2.6 M aqueous nitric acid, with one solvent exchange, followed bysonication in saturated NaOH in ethanol at room temperature for 12hours, then neutralization by refluxing in 6M aqueous HCl for 12 hours,removal from the aqueous medium and baking in a hydrogen gas atmosphereat 850 C. in 1 atm H₂ gas (flowing at 1-10 sccm through a 1″ quartztube) for 2 hours, detailed TEM, SEM and Raman spectral examinationshowed it to be >99% pure, with the dominant impurity being a fewcarbon-encapsulated Ni/Co particles. (See FIGS. 3A, 3B, 3C)

In another embodiment, a slightly basic solution (e.g., pH ofapproximately 8-12) may also be used in the saponification step. Theinitial cleaning in 2.6 M HNO₃ converts amorphous carbon in the rawmaterial to various sizes of linked polycyclic compounds, such as fulvicand humic acids, as well as larger polycyclic aromatics with variousfunctional groups around the periphery, especially the carboxylic acidgroups. The base solution ionizes most of the polycyclic compounds,making them more soluble in aqueous solution. In a preferred process,the nanotube containing felts are refluxed in 2-5 M HNO₃ for 6-15 hoursat approximately 110°-125° C. Purified nanotubes may be filtered andwashed with 10 mM NaOH solution on a 3 micron pore size TSTP Isoporefilter. Next, the filtered nanotubes polished by stirring them for 30minutes at 60° C. in a S/N (Sulfuric acid/Nitric acid) solution. In apreferred embodiment, this is a 3:1 by volume mixture of concentratedsulfuric acid and nitric acid. This step removes essentially all theremaining material from the tubes that is produced during the nitricacid treatment.

Once the polishing is complete, a four-fold dilution in water is made,and the nanotubes are again filtered on the 3 micron pore size TSTPIsopore filter. The nanotubes are again washed with a 10 mM NaOHsolution. Finally, the nanotubes are stored in water, because drying thenanotubes makes it difficult to resuspend them.

The conditions may be further optimized for particular uses, but thisbasic approach by refluxing in oxidizing acid has been shown to besuccessful. Purification according to this method will producesingle-wall nanotubes for use as catalysts, as components in compositematerials, or as a starting material in the production of tubular carbonmolecules and continuous macroscopic carbon fiber of single-wallnanotube molecules.

Single-Wall Carbon Nanotube Molecules

Single-wall carbon nanotubes produced by prior methods are so long andtangled that it is very difficult to purify them, or manipulate them.However, the present invention provides for cutting them into shortenough lengths that they are no longer tangled and annealing the openends closed. The short, closed tubular carbon molecules may be purifiedand sorted very readily using techniques that are similar to those usedto sort DNA or size polymers. Thus, this invention effectively providesa whole new class of tubular carbon molecules.

Preparation of homogeneous populations of short carbon nanotubemolecules may be accomplished by cutting and annealing (reclosing) thenanotube pieces followed by fractionation. The cutting and annealingprocesses may be carried out on a purified nanotube bucky paper, onfelts prior to purification of nanotubes or on any material thatcontains single-wall nanotubes. When the cutting and annealing processis performed on felts, it is preferably followed by oxidativepurification, and optionally saponification, to remove amorphous carbon.Preferably, the starting material for the cutting process is purifiedsingle-wall nanotubes, substantially free of other material.

The short nanotube pieces can be cut to a length or selected from arange of lengths, that facilitates their intended use. For applicationsinvolving the individual tubular molecules per se (e.g., derivatives,nanoscale conductors in quantum devices, i.e., molecular wire), thelength can be from just greater than the diameter of the tube up toabout 1,000 times the diameter of the tube. Typical tubular moleculeswill be in the range of from about 5 to 1,000 nanometers or longer. Formaking template arrays useful in growing carbon fibers of SWNT asdescribed below, lengths of from about 50 to 500 nm are preferred.

Any method of cutting that achieves the desired length of nanotubemolecules without substantially affecting the structure of the remainingpieces can be employed. The preferred cutting method employs irradiationwith high mass ions. In this method, a sample is subjected to a fast ionbeam, e.g., from a cyclotron, at energies of from about 0.1 to 10giga-electron volts. Suitable high mass ions include those over about150 AMU's such as bismuth, gold, uranium and the like.

Preferably, populations of individual single-wall nanotube moleculeshaving homogeneous length are prepared starting with a heterogeneousbucky paper and cutting the nanotubes in the paper using a gold (Au⁺³³)fast ion beam. In a typical procedure, the bucky paper (about 100 micronthick) is exposed to ⁻10¹² fast ions per cm², which produces severelydamaged nanotubes in the paper, on average every 100 nanometers alongthe length of the nanotubes. The fast ions create damage to the buckypaper in a manner analogous to shooting 10-100 nm diameter “bulletholes” through the sample. The damaged nanotubes then can be annealed(closed) by heat sealing of the tubes at the point where ion damageoccurred, thus producing a multiplicity of shorter nanotube molecules.At these flux levels, the shorter tubular molecules produced will have arandom distribution of cut sizes with a length peak near about 100 nm.Suitable annealing conditions are well known in the fullerene art, suchas for example, baking the tubes in vacuum or inert gas at 1200° C. for1 hour.

The SWNTs may also be cut into shorter tubular molecules byintentionally incorporating defect-producing atoms into the structure ofthe SWNT during production. These defects can be exploited chemically(e.g., oxidatively attacked) to cut the SWNT into smaller pieces. Forexample, incorporation of 1 boron atom for every 1000 carbon atoms inthe original carbon vapor source can product SWNTs with built-in weakspots for chemical attack.

Cutting may also be achieved by sonicating a suspension of SWNTs in asuitable medium such as liquid or molten hydrocarbons. One suchpreferred liquid is 1,2-dichloreothane. Any apparatus that producessuitable acoustic energy can be employed. One such apparatus is theCompact Cleaner (One Pint) manufactured by Cole-Parmer, Inc. This modeloperates at 40 KHz and has an output of 20 W. The sonication cuttingprocess should be continued at a sufficient energy input and for asufficient time to substantially reduce the lengths of tubes, ropes orcables present in the original suspension. Typically times of from about10 minutes to about 24 hours can be employed depending on the nature ofthe starting material and degree of length reduction sought.

In another embodiment, sonication may be used to create defects alongthe rope lengths, either by the high temperatures and pressures createdin bubble collapse (˜5000° C. and ˜1000 atm), or by the attack of freeradicals produced by sonochemistry. These defects are attacked by S/N tocleanly cut the nanotube, exposing the tube underneath for more damageand cutting. As the acid attacks the tube, the tube is completely cutopen and slowly etches back, its open end being unable to reclose at themoderate temperature. In a preferred process, the nanotubes are bathsonocated while being stirred in 40-45° C. S/N for 24 hours. Next, thenanotubes are stirred with no sonication in the S/N for 2 hours at40-45° C. This is to attack, with the S/N, all the defects created bythe sonication without creating more defects. Then, the nanotubes arediluted four-fold with water, and then filtered using a 0.1 micron poresize VCTP filter. Next, the nanotubes are filtered and washed with a 10mM NaOH solution on the VCTP filter. The nanotubes are polished bystirring them for 30 minutes at 70° C. in a S/N solution. The polishednanotubes are diluted for four-fold with water, filtered using the 0.1micron pore size VCTP filters, then filtered and washed with 10 mM NaOHon a 0.1 micron pore size VCTP filter, and then stored in water.

Oxidative etching, e.g., with highly concentrated nitric acid, can alsobe employed to effect cutting of SWNTs into shorter lengths. Forexample, refluxing SWNT material in concentrated HNO₃ for periods ofseveral hours to 1 or 2 days will result in significantly shorter SWNTs.The rate of cutting by this mechanism is dependent on the degree ofhelicity of the tubes. This fact may be utilized to facilitateseparation of tubes by type, i.e., (n,n) from (m,n).

Length distribution shortens systematically with exposure time to theacid. For example, in a 3/1 concentrated sulfuric/nitric acid at 70° C.the average cut nanotube shortens at a rate of approximately 100 nmhr⁻¹. In a 4/1 sulfuric acid/30% aqueous hydrogen peroxide (“piranha”)mixture at 70° C., the shortening rate is approximately 200 nm hr⁻¹. Theetching rate is sensitive to the chiral index of the nanotubes (n,m),with all “arm-chair” tubes (m=x) having a distinct chemistry from the“zig-zag” tubes (m=0), and to a lesser extend with tubes of intermediatehelical angle (n≈m).

The cleaned nanotube material may be cut into 50-500 nm lengths,preferably 100-300 nm lengths, by this process. The resulting pieces mayform a colloidal suspension in water when mixed with a surfactant suchas Triton X-100™ (Aldrich, Milwaukee, Wis.). These sable suspensionspermit a variety of manipulations such as sorting by length using fieldflow fractionation, and electrodeposition on graphite followed by AFMimaging.

In another embodiment, SWNTs can be cut using electron beam cuttingapparatus in the known manner.

Combination of the foregoing cutting techniques can also be employed.

Homogeneous populations of single-walled nanotubes may be prepared byfractionating heterogeneous nanotube populations after annealing. Theannealed nanotubes may be disbursed in an aqueous detergent solution oran organic solvent for the fractionation. Preferably the tubes will bedisbursed by sonication in benzene, toluene, xylene or moltennaphthalene. The primary function of this procedure is to separatenanotubes that are held together in the form of ropes or mats by van derWaals forces. Following separation into individual nanotubes, thenanotubes may be fractionated by size by using fractionation procedureswhich are well known, such as procedures for fractionating DNA orpolymer fractionation procedures. Fractionation also can be performed ontubes before annealing, particularly if the open ends have substituents(carboxy, hydroxy, etc.), that facilitate the fractionation either bysize or by type. Alternatively, the closed tubes can be opened andderivatized to provide such substituents. Closed tubes can also bederivatized to facilitate fractionation, for example, by addingsolubilizing moieties to the end caps.

Electrophoresis is one such technique well suited to fractionation ofSWNT molecules since they can easily be negatively charged. It is alsopossible to take advantage of the different polarization and electricalproperties of SWNTs having different structure type (e.g., arm chair andzig-zag) to separate the nanotubes by type. Separation by type can alsobe facilitated by derivatizing the mixture of molecules with a moietythat preferentially bonds to one type of structure.

In a typical example, a 100 micron thick mat of black bucky paper, madeof nanotubes purified by refluxing in nitric acid for 48 hours wasexposed for 100 minutes to a 2 GeV beam of gold (Au⁺³³) ions in theTexas A&M Superconducting Cyclotron Facility (net flux of up to 10¹²ions per cm²). The irradiated paper was baked in a vacuum at 1200° C.for 1 hr to seal off the tubes at the “bullet holes,” and then dispersedin toluene while sonicating. The resultant tubular molecules wereexamined via SEM, AFM and TEM.

The procedures described herein produce tubular molecules that aresingle-wall nanotubes in which the cylindrical portion is formed from asubstantially defect-free sheet of graphene (carbon in the form ofattached hexagons) rolled up and joined at the two edges parallel to itslong axis. The nanotube can have a fullerene cap (e.g., hemispheric) atone end of the cylinder and a similar fullerene cap at the other end.One or both ends can also be open. Prepared as described herein, theseSWNT molecules are substantially free of amorphous carbon. Thesepurified nanotubes are effectively a whole new class of tubularmolecules.

In general the length, diameter and helicity of these molecules can becontrolled to any desired value. Preferred lengths are up to 10⁶hexagons; preferred diameters are about 5 to 50 hexagon circumference;and the preferred helical angle is 0° to 30°.

Preferably, the tubular molecules are produced by cutting and annealingnanotubes of predominately arm-chair (n,n) configuration, which may beobtained by purifying material produced according to the methodsdiscussed above. These (n,n) carbon molecules, purified as describedherein, are the first truly “metallic molecules.” These molecules areuseful for making electrical connectors for devices such as integratedcircuits or semiconductor chips used in computers because of the highelectrical conductivity and small size of the carbon molecule. SWNTmolecules are also useful as components of electrical devices wherequantum effects dominate at room temperature, for example, resonanttunneling diodes. The metallic carbon molecules are useful as antennasat optical frequencies, and as probes for scanning probe microscopy suchas are used in scanning tunneling microscopes (STM) and atomic forcemicroscopes (AFM). The semiconducting SWNT structures, an (m, n) tubewherein m≠n may be used, with appropriate doping, as nanoscalesemiconductor devices such as transistors.

The tubular carbon molecules of this invention may also be used in RFshielding applications, e.g., to make microwave absorbing materials.

Single-walled nanotube molecules may serve as catalysts in any of thereaction known to be catalyzed as fullerenes, with the added benefitsthat the linear geometry of the molecule provides. The carbon nanotubesare also useful as supports for catalysts used in industrial andchemical processes such as hydrogenation, reforming and crackingcatalysts. Materials including the SWNT molecules can also be used ashydrogen storage devices in battery and fuel cell devices.

The tubular carbon molecules produced according to this invention can bechemically derivatized at their ends (which may be made either open orclosed with a hemi-fullerene dome). Derivatization at the fullerene capstructures is facilitated by the well-known reactivity of thesestructures. See, “The Chemistry of Fullerenes” R. Taylor ed., Vol. 4 ofthe advanced Series in Fullerenes, World Scientific Publishers,Singapore, 1995; A. Hirsch, “The Chemistry of the Fullerenes,” Thieme,1994. Alternatively, the fullerene caps of the single-walled nanotubesmay be removed at one or both ends of the tubes by short exposure tooxidizing conditions (e.g., with nitric acid or O₂/CO₂) sufficient toopen the tubes but not etch them back too far, and the resulting opentube ends maybe derivatized using known reaction schemes for thereactive sites at the graphene sheet edge.

In general, the structure of such molecules can be shown as follows:

where

is a substantially defect-free cylindrical graphene sheet (whichoptionally can be doped with non-carbon atoms) having from about 10² toabout 10⁶ carbon atoms, and having a length of from about 5 to about1000 nm, preferably about 5 to about 500 nm;

is a fullerene cap that fits perfectly on the cylindrical graphenesheet, has at least six pentagons and the remainder hexagons andtypically has at least about 30 carbon atoms;

-   -   n is a number from 0 to 30, preferably 0 to 12; and    -   R, R¹, R², R³, R⁴, and R⁵ each may be independently selected        from the group consisting of hydrogen; alkyl, acyl, aryl,        aralkyl, halogen; substituted or unsubstituted thiol;        unsubstituted or substituted amino; hydroxy, and OR′ wherein R′        is selected from the group consisting of hydrogen, alkyl, acyl,        aryl aralkyl, unsubstituted or substituted amino; substituted or        unsubstituted thiol; and halogen; and a linear or cyclic carbon        chain optionally interrupted with one or more heteroatom, and        optionally substituted with one or more ═O, or ═S, hydroxy, an        aminoalkyl group, an amino acid, or a peptide of 2-8 amino        acids.

The following definitions are used herein.

The term “alkyl” as employed herein includes both straight and branchedchain radicals, for example methyl, ethyl, propyl, isopropyl, butyl,t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl, 4,4-dimethylpentyl,octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl, dodecyl, thevarious branched chain isomers thereof. The chain may be linear orcyclic, saturated or unsaturated, containing, for example, double andtriple bonds. The alkyl chain may be interrupted or substituted with,for example, one or more halogen, oxygen, hydroxy, silyl, amino, orother acceptable substituents.

The term “acyl” as used herein refers to carbonyl groups of the formula—COR wherein R may be any suitable substituent such as, for example,alkyl, aryl, aralkyl, halogen; substituted or unsubstituted thiol;unsubstituted or substituted amino, unsubstituted or substituted oxygen,hydroxy, or hydrogen.

The term “aryl” as employed herein refers to monocyclic, bicyclic ortricyclic aromatic groups containing from 6 to 14 carbons in the ringportion, such as phenyl, naphthyl, substituted phenyl, or substitutednaphthyl, wherein the substituent on either the phenyl or naphthyl maybe for example C₁₋₄ alkyl, halogen, C₁₋₄ alkoxy, hydroxy or nitro.

The term “aralkyl” as used herein refers to alkyl groups as discussedabove having an aryl substituent, such as benzyl, p-nitrobenzyl,phenylethyl, diphenylmethyl, and triphenylmethyl.

The term “aromatic or non-aromatic ring” as used herein includes 5-8membered aromatic and non-aromatic rings uninterrupted or interruptedwith one or more heteroatom, for example O, S, SO, SO₂, and N, or thering may be unsubstituted or substituted with, for example, halogen,alkyl, acyl, hydroxy, aryl, and amino, said heteroatom and substituentmay also be substituted with, for example, alkyl, acyl, aryl, oraralkyl.

The term “linear or cyclic” when used herein includes, for example, alinear chain which may optionally be interrupted by an aromatic ornon-aromatic ring. Cyclic chain includes, for example, an aromatic ornon-aromatic ring which may be connected to, for example, a carbon chainwhich either precedes or follows the ring.

The term “substituted amino” as used herein refers to an amino which maybe substituted with one or more substituent, for example, alkyl, acyl,aryl, aralkyl, hydroxy, and hydrogen.

The term “substituted thiol” as used herein refers to a thiol which maybe substituted with one or more substituent, for example, alkyl, acyl,aryl, aralkyl, hydroxy, and hydrogen.

Typically, open ends may contain up to about 20 substituents and closedends may contain up to about 30 substituents. It is preferred, due tostearic hindrance, to employ up to about 12 substituents per end.

In addition to the above described external derivatization, the SWNTmolecules of the present invention can be modified endohedrally, i.e.,by including one or more metal atoms inside the structure, as is knownin the endohedral fullerene art. It is also possible to “load” the SWNTmolecule with one or more smaller molecules that do not bond to thestructures, e.g., C₆₀, to permit molecular switching as the C₆₀ buckyball shuttles back and forth inside the SWNT molecule under theinfluence of external fields or forces.

To produce endohedral tubular carbon molecules, the internal species(e.g., metal atom, bucky ball molecules) can either be introduced duringthe SWNT formation process or added after preparation of the tubularmolecules. Incorporation of metals into the carbon source that isevaporated to form the SWNT material is accomplished in the mannerdescribed in the prior art for making endohedral metallofullerenes.Bucky balls, i.e., spheroidal fullerene molecules, are preferably loadedinto the tubular carbon molecules of this invention by removing one orboth end caps of the tubes employing oxidation etching described above,and adding an excess of bucky ball molecules (e.g., C₆₀, C₇₀) by heatingthe mixture (e.g., from about 500 to about 600° C.) in the presence ofC₆₀ to C₇₀ containing vapor for an equilibration period (e.g., fromabout 12 to about 36 hours). A significant proportion (e.g., from a fewtenths of a percent up to about 50 percent or more) of the tubes willcapture a bucky ball molecule during this treatment. By selecting therelative geometry of the tube and ball this process can be facilitated.For example, C₆₀ and C₇₀ fit very nicely in a tubular carbon moleculecut from a (10,10) SWNT (I.D.≅1 nm). After the loading step, the tubescontaining bucky ball molecules can be closed (annealed shut) by heatingunder vacuum to about 1100° C. Bucky ball encapsulation can be confirmedby microscopic examination, e.g., by TEM.

Endohedrally loaded tubular carbon molecules can then be separated fromempty tubes and any remaining loading materials by taking advantage ofthe new properties introduced into the loaded tubular molecules, forexample, where the metal atom imparts magnetic or paramagneticproperties to the tubes, or the bucky ball imparts extra mass to thetubes. Separation and purification methods based on these properties andothers will be readily apparent to those skilled in the art.

Fullerene molecules like C₆₀ or C₇₀ will remain inside the properlyselected tubular molecule (e.g., one based on (10,10) SWNTs) becausefrom an electronic standpoint (e.g., by van der Waals interaction) thetube provides an environment with a more stable energy configurationthan that available outside the tube.

Molecular Arrays of Single-Wall Carbon Nanotubes

An application of particular interest for a homogeneous population ofSWNT molecules is production of a substantially two-dimensional arraymade up of single-walled nanotubes aggregating (e.g., by van der Waalsforces) in substantially parallel orientation to form a monolayerextending in directions substantially perpendicular to the orientationof the individual nanotubes. Such monolayer arrays can be formed byconventional techniques employing “self-assembled monolayers” (SAM) orLangmiur-Blodgett films, see Hirch, pp. 75-76. Such a molecular array isillustrated schematically in FIG. 4. In this figure, nanotubes 1 arebound to a substrate 2 having a reactive coating 3 (e.g., gold).

Typically, SAMs are created on a substrate which can be a metal (such asgold, mercury or ITO (indium-tin-oxide)). The molecules of interest,here the SWNT molecules, are linked (usually covalently) to thesubstrate through a linker moiety such as —S—, —S—(CH₂)_(n)—NH—,—SiO₃(CH₂)₃NH— or the like. The linker moiety may be bound first to thesubstrate layer or first to the SWNT molecule (at an open or closed end)to provide for reactive self-assembly. Langmiur-Blodgett films areformed at the interface between two phases, e.g., a hydrocarbon (e.g.,benzene or toluene) and water. Orientation in the film is achieved byemploying molecules or linkers that have hydrophilic and lipophilicmoieties at opposite ends.

The configuration of the SWNT molecular array may be homogenous orheterogeneous depending on the use to which it will be put. Using SWNTmolecules of the same type and structure provides a homogeneous array ofthe type shown in FIG. 4. By using different SWNT molecules, either arandom or ordered heterogeneous structure can be produced. An example ofan ordered heterogeneous arrays is shown in FIG. 5 where tubes 4 are(n,n), i.e., metallic in structure and tubes 5 are (m,n), i.e.,insulating. This configuration can be achieved by employing successivereactions after removal of previously masked areas of the reactivesubstrate.

Arrays containing from 10³ up to 10¹⁰ and more SWNT molecules insubstantially parallel relationships can be used per se as a nanoporousconductive molecular membrane, e.g., for use in batteries such as thelithium ion battery. This membrane can also be used (with or withoutattachment of a photoactive molecule such as cis-(bisthiacyanatobis(4,4′-dicarboxy-2,2′-bipyridine Ru(II)) to produce a highly efficientphoto cell of the type shown in U.S. Pat. No. 5,084,365.

One preferred use of the SWNT molecular arrays of the present inventionis to provide a “seed” or template for growth of macroscopic carbonfiber of single-wall carbon nanotubes as described below. The use of amacroscopic cross section in this template is particularly useful forkeeping the live (open) end of the nanotubes exposed to feedstock duringgrowth of the fiber. The template array of this invention can be used asformed on the original substrate, cleaved from its original substrateand used with no substrate (the van der Waals forces will hold ittogether) or transferred to a second substrate more suitable for theconditions of fiber growth.

Where the SWNT molecular array is to be used as a seed or template forgrowing macroscopic carbon fiber as described below, the array need notbe formed as a substantially two-dimensional array. Any form of arraythat presents at its upper surface a two-dimensional array can beemployed. In the preferred embodiment, the template molecular array is amanipulatable length of macroscopic carbon fiber as produced below.

Another method for forming a suitable template molecular array involvesemploying purified bucky paper as the starting material. Upon oxidativetreatment of the bucky paper surface (e.g., with O₂/CO₂ at about 500°C.), the sides as well as ends of SWNTs are attacked and many tubeand/or rope ends protrude up from the surface of the paper. Disposingthe resulting bucky paper in an electric field (e.g., 100 V/cm² resultsin the protruding tubes and or ropes aligning in a directionsubstantially perpendicular to the paper surface. These tubes tend tocoalesce due to van der Waals forces to form a molecular array.

Alternatively, a molecular array of SWNTs can be made by “combing” thepurified bucky paper starting material. “Combing” involves the use of asharp microscopic tip such as the silicon pyramid on the cantilever of ascanning force microscope (“SFM”) to align the nanotubes. Specifically,combing is the process whereby the tip of an SFM is systematicallydipped into, dragged through, and raised up from a section of buckypaper. An entire segment of bucky paper could be combed, for example,by: (i) systematically dipping, dragging, raising and moving forward anSFM tip along a section of the bucky paper, (ii) repeating the sequencein (i) until completion of a row; and (iii) repositioning the tip alonganother row and repeating (i) and (ii). In a preferred method ofcombing, the section of bucky paper of interest is combed through as insteps (i)-(iii) above at a certain depth and then the entire process isrepeated at another depth. For example, a lithography script can bewritten and run which could draw twenty lines with 0.5 μm spacing in a10×10 μm square of bucky paper. The script can be run seven times,changing the depth from zero to three μm in 0.5 μm increments.

Large arrays (i.e., >10⁶ tubes) also can be assembled using nanoprobesby combining smaller arrays or by folding linear collections of tubesand/or ropes over (i.e., one folding of a collection of n tubes resultsin a bundle with 2 n tubes).

Macroscopic arrays can also be formed by providing a nanoscale microwellstructure (e.g., a SiO₂ coated silicon wafer with >10⁶ rectangular 10 nmwide, 10 nm deep wells formed in the surface by electron beamlithographic techniques). A suitable catalyst metal cluster (orprecursor) is deposited in each well and a carbon-containing feedstockis directed towards the array under growth conditions described below toinitiate growth of SWNT fibers from the wells. Catalysts in the form ofpreformed nanoparticles (i.e., a few nanometers in diameter) asdescribed in Dai et al., “Single-Wall Nanotubes Produced byMetal-Catalyzed Disproportionation of Carbon Monoxide,” Chem. Phys.Lett. 260 (1996), 471-475 (“Dai”) can also be used in the wells. Anelectric field can be applied to orient the fibers in a directionsubstantially perpendicular to the wafer surface.

Growth of Continuous Carbon Fiber from SWNT Molecular Arrays

The present invention provides method for growing continuous carbonfiber from SWNT molecular arrays to any desired length. The carbon fiberwhich comprises an aggregation of substantially parallel carbonnanotubes may be produced according to this invention by growth(elongation) of a suitable seed molecular array. The preferred SWNTmolecular array is produced as described above from a SAM of SWNTmolecules of substantially uniform length. As used herein, the term“macroscopic carbon fiber” refers to fibers having a diameter largeenough to be physically manipulated, typically greater than about 1micron and preferably greater than about 10 microns.

The first step in the growth process is to open the growth end of theSWNTs in the molecular array. This can be accomplished as describedabove with an oxidative treatment. Next, a transition metal catalyst isadded to the open-ended seed array. The transition metal catalyst can beany transition metal that will cause conversion of the carbon-containingfeedstock described below into highly mobile carbon radicals that canrearrange at the growing edge to the favored hexagon structure. Suitablematerials include transition metals, and particularly the Group VI orVIII transition metals, i.e., chromium (Cr), molybdenum (Mo), tungsten(W), iron (Fe), cobalt (Co), nickel (NI), ruthenium (Ru), rhodium (Rh),palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt). Metals fromthe lanthanide and actinide series may also be used. Preferred are Fe,Ni, Co and mixtures thereof. Most preferred is a 50/50 mixture (byweight) of Ni and Co.

The catalyst should be present on the open SWNT ends as a metal clustercontaining from about 10 metal atoms up to about 200 metal atoms(depending on the SWNT molecule diameter). Typically, the reactionproceeds most efficiently if the catalyst metal cluster sits on top ofthe open tube and does not bridge over more than one or two tubes.Preferred are metal clusters having a cross-section equal to from about0.5 to about 1.0 times the tube diameter (e.g., about 0.7 to 1.5 nm).

In the preferred process, the catalyst is formed, in situ, on the opentube ends of the molecular array by a vacuum deposition process. Anysuitable equipment, such as that used in Molecular Beam Epitaxy (MBE)deposition, can be employed. One such device is a Küdsen Effusion SourceEvaporator. It is also possible to effect sufficient deposition of metalby simply heating a wire in the vicinity of the tube ends (e.g., a Ni/COwire or separate Ni and CO wires) to a temperature below the meltingpoint at which enough atoms evaporate from one wire surface (e.g., fromabout 900 to about 1300° C.). The deposition is preferably carried outin a vacuum with prior outgassing. Vacuums of about 10⁻⁶ to 10⁻⁴ Torrare suitable. The evaporation temperature should be high enough toevaporate the metal catalyst. Typically, temperatures in the range of1500 to 2000° C. are suitable for the Ni/Co catalyst of the preferredembodiment. In the evaporation process, the metal is typically depositedas monolayers of metal atoms. From about 1-10 monolayers will generallygive the required amount of catalyst. The deposition of transition metalclusters on the open tube tops can also be accomplished by laservaporization of metal targets in a catalyst deposition zone.

The actual catalyst metal cluster formation at the open tube ends iscarried out by heating the tube ends to a temperature high enough toprovide sufficient species mobility to permit the metal atoms to findthe open ends and assemble into clusters, but not so high as to effectclosure of the tube ends. Typically, temperatures of up to about 500° C.are suitable. Temperatures in the range of about 400-500° C. arepreferred for the Ni/Co catalysts system of one preferred embodiment.

In a preferred embodiment, the catalyst metal cluster is deposited onthe open nanotube end by a docking process that insures optimum locationfor the subsequent growth reaction. In this process, the metal atoms aresupplied as described above, but the conditions are modified to providereductive conditions, e.g., at 800° C., 10 millitorr of H₂ for 1 to 10minutes. There conditions cause the metal atom clusters to migratethrough the system in search of a reactive site. During the reductiveheating the catalyst material will ultimately find and settle on theopen tube ends and begin to etch back the tube. The reduction periodshould be long enough for the catalyst particles to find and begin toetch back the nanotubes, but not so long as to substantially etch awaythe tubes. By changing to the above-described growth conditions, theetch-back process is reversed. At this point, the catalyst particles areoptimally located with respect to the tube ends since they already werecatalytically active at those sites (albeit in the reverse process).

The catalyst can also be supplied in the form of catalyst precursorswhich convert to active form under growth conditions such as oxides,other salts or ligand stabilized metal complexes. As an example,transition metal complexes with alkylamines (primary, secondary ortertiary) can be employed. Similar alkylamine complexes of transitionmetal oxides also can be employed.

In an alternative embodiment, the catalyst may be supplied as preformednanoparticles (i.e., a few nanometers in diameter) as described in Dai.

In the next step of the process of the present invention, the SWNTmolecular array with catalyst deposited on the open tube ends issubjected to tube growth (extension) conditions. This may be in the sameapparatus in which the catalyst is deposited or a different apparatus.The apparatus for carrying out this process will require, at minimum, asource of carbon-containing feedstock and a means for maintaining thegrowing end of the continuous fiber at a growth and annealingtemperature where carbon from the vapor can be added to the growing endsof the individual nanotubes under the direction of the transition metalcatalyst. Typically, the apparatus will also have means for continuouslycollecting the carbon fiber. The process will be described forillustration purposes with reference to the apparatus shown in FIGS. 6and 7.

The carbon supply necessary to grow the SWNT molecular array into acontinuous fiber is supplied to the reactor 10, in gaseous form throughinlet 11. The gas stream should be directed towards the front surface ofthe growing array 12. The gaseous carbon-containing feedstock can be anyhydrocarbon or mixture of hydrocarbons including alkyls, acyls, aryls,aralkyls and the like, as defined above. Preferred are hydrocarbonshaving from about 1 to 7 carbon atoms. Particularly preferred aremethane, ethane, ethylene, acetylene, acetone, propane, propylene andthe like. Most preferred is ethylene. Carbon monoxide may also be usedand in some reactions is preferred. Use of CO feedstock with preformedMo-based nano-catalysts is believed to follow a different reactionmechanism than that proposed for in situ-formed catalyst clusters. SeeDai.

The feedstock concentration is preferably as chosen to maximize the rateof reaction, with higher concentrations of hydrocarbon giving fastergrowth rates. In general, the partial pressure of the feedstock material(e.g., ethylene) can be in the 0.001 to 1000.0 Torr range, with valuesin the range of about 1.0 to 10 Torr being preferred. The growth rate isalso a function of the temperature of the growing array tip as describedbelow, and as a result growth temperatures and feed stock concentrationcan be balanced to provide the desired growth rates.

It is not necessary or preferred to preheat the carbon feedstock gas,since unwanted pyrolysis at the reactor walls can be minimized thereby.The only heat supplied for the growth reaction should be focused at thegrowing tip of the fiber 12. The rest of the fiber and the reactionapparatus can be kept at room temperature. Heat can be supplied in alocalized fashion by any suitable means. For small fibers (<1 mm indiameter), a laser 13 focused at the growing end is preferred (e.g., aC-W laser such as an argon ion laser beam at 514 nm). For larger fibers,heat can be supplied by microwave energy of R-F energy, again localizedat the growing fiber tip. Any other form of concentrated electromagneticenergy that can be focused on the growing tip can be employed (e.g.,solar energy). Care should be taken, however, to avoid electromagneticradiation that will be absorbed to any appreciable extent by thefeedstock gas.

The SWNT molecular array tip should be heated to a temperaturesufficient to cause growth and efficient annealing of defects in thegrowing fiber, the forming a growth and annealing zone at the tip. Ingeneral, the upper limit of this temperature is governed by the need toavoid pyrolysis of the feedstock and fouling of the reactor orevaporation of the deposited metal catalyst. For most feedstocks, thisis below about 1300° C. The lower end of the acceptable temperaturerange is typically about 500° C., depending on the feedstock andcatalyst efficiency. Preferred are temperatures in the range of about500° C. to about 1200° C. More preferred are temperatures in the rangeof from about 700° C. to about 1200° C. Temperatures in the range ofabout 900° C. to about 1100° C. are the most preferred, since at thesetemperatures the best annealing of defects occurs. The temperature atthe growing end of the cable is preferably monitored by, and controlledin response to, an optical pyrometer 14, which measures theincandescence produced. While not preferred due to potential foulingproblems, it is possible under some circumstance to employ an inertsweep gas such as argon or helium.

In general, pressure in the growth chamber can be in the range of 1millitorr to about 1 atmosphere. The total pressure should be kept at 1to 2 times the partial pressure of the carbon feedstock. A vacuum pump15 may be provided as shown. It may be desirable to recycle thefeedstock mixture to the growth chamber. As the fiber grows it can bewithdrawn from the growth chamber 16 by a suitable transport mechanismsuch as drive roll 17 and idler roll 18. The growth chamber 16 is indirect communication with a vacuum feed lock zone 19.

The pressure in the growth chamber can be brought up to atmospheric, ifnecessary, in the vacuum feed lock by using a series of chambers 20.Each of these chambers is separated by a loose TEFLON O-ring seal 21surrounding the moving fiber. Pumps 22 effect the differential pressureequalization. A take-up roll 23 continuously collects the roomtemperature carbon fiber cable. Product output of this process can be inthe range of 10⁻³ to 10¹ feet per minute or more. By this process, it ispossible to produce tons per day of continuous carbon fiber made up ofSWNT molecules.

Growth of the fiber can be terminated at any stage (either to facilitatemanufacture of a fiber of a particular length or when too many defectsoccur). To restart growth, the end may be cleaned (i.e., reopened) byoxidative etching (chemically or electrochemically). The catalystparticles can then be reformed on the open tube ends, and growthcontinued.

The molecular array (template) may be removed from the fiber before orafter growth by macroscopic physical separation means, for example bycutting the fiber with scissors to the desired length. Any section fromthe fiber may be used as the template to initiate production of similarfibers.

The continuous carbon fiber of the present invention can also be grownfrom more than one separately prepared molecular array or template. Themultiple arrays can be the same or different with respect to the SWNTtype of geometric arrangement in the array. Large cable-like structureswith enhanced tensile properties can be grown from a number of smallerseparate arrays as shown in FIG. 8. In addition to the masking andcoating techniques described above, it is possible to prepare acomposite structure, for example, by surrounding a central core array ofmetallic SWNTs with a series of smaller circular non-metallic SWNTarrays arranged in a ring around the core array as shown in FIG. 9.

Not all the structures contemplates by this invention need by round oreven symmetrical in two-dimensional cross section. It is even possibleto align multiple molecular array seed templates in a manner as toinduce nonparallel growth of SWNTs in some portions of the compositefiber, thus producing a twisted, helical rope, for example. It is alsopossible to catalytically grow macroscopic carbon fiber in the presenceof an electric field to aid in alignment of the SWNTs in the fibers, asdescribed above in connection with the formation of template arrays.

Random Growth of Carbon Fibers From SWNTs

While the continuous growth of ordered bundles of SWNTs described aboveis desirable for many applications, it is also possible to produceuseful compositions comprising a randomly oriented mass of SWNTs, whichcan include individual tubes, ropes and/or cables. The random growthprocess has the ability to produce large quantities, i.e., tons per day,of SWNT material.

In general the random growth method comprises providing a plurality ofSWNT seed molecules that are supplied with a suitable transition metalcatalyst as described above, and subjecting the seed molecules to SWNTgrowth conditions that result in elongation of the seed molecule byseveral orders of magnitude, e.g., 10² to 10¹⁰ or more times itsoriginal length.

The seed SWNT molecules can be produced as described above, preferablyin relatively short lengths, e.g., by cutting a continuous fiber orpurified bucky paper. In a preferred embodiment, the seed molecules canbe obtained after one initial run from the SWNT felt produced by thisrandom growth process (e.g., by cutting). The lengths do not need to beuniform and generally can range from about 5 nm to 10 μm in length.

These SWNT seed molecules may be formed on macroscale or nanoscalesupports that do not participate in the growth reaction. In anotherembodiment, SWNTs or SWNT structures can be employed as the supportmaterial/seed. For example, the self assembling techniques describedbelow can be used to form a three-dimensional SWNT nanostructure.Nanoscale powders produced by these technique have the advantage thatthe support material can participate in the random growth process.

The supported or unsupported SWNT seed materials can be combined with asuitable growth catalyst as described above, by opening SWNT moleculeends and depositing a metal atom cluster. Alternatively, the growthcatalyst can be provided to the open end or ends of the seed moleculesby evaporating a suspension of the seeds in a suitable liquid containinga soluble or suspended catalyst precursor. For example, when the liquidis water, soluble metal salts such as Fe(NO₃)₃, Ni(NO₃)₂ or CO(NO₃)₂ andthe like may be employed as catalyst precursors. In order to insure thatthe catalyst material is properly positioned on the open end(s) of theSWNT seed molecules, it may be necessary in some circumstances toderivitize the SWNT ends with a moiety that binds the catalystnanoparticle or more preferably a ligand-stabilized catalystnanoparticle.

In the first step of the random growth process the suspension of seedparticles containing attached catalysts or associated with dissolvedcatalyst precursors is injected into an evaporation zone where themixture contacts a sweep gas flow and is heated to a temperature in therange of 250-500° C. to flash evaporate the liquid and provide anentrained reactive nanoparticle (i.e., seed/catalyst). Optionally thisentrained particle stream is subjected to a reduction step to furtheractivate the catalyst (e.g., heating from 300-500° C. in H₂). Acarbonaceous feedstock gas, of the type employed in the continuousgrowth method described above, is then introduced into the sweepgas/active nanoparticle stream and the mixture is carried by the sweepgas into and through a growth zone.

The reaction conditions for the growth zone are as described above,i.e., 500-1000° C. and a total pressure of about one atmosphere. Thepartial pressure of the feedstock gas (e.g., ethylene, CO) can be in therange of about 1 to 100 Torr. The reaction is preferably carried out ina tubular reactor through which a sweep gas (e.g., argon) flows.

The growth zone may be maintained at the appropriate growth temperatureby 1) preheating the feedstock gas, 2) preheating the sweep gas, 3)externally heating the growth zone, 4) applying localized heating in thegrowth zone, e.g., by laser or induction coil, or any combination of theforegoing.

Downstream recovery of the product produced by this process can beeffected by known means such as filtration, centrifugation and the like.Purification may be accomplished as described above. Felts made by thisrandom growth process can be used to make composites, e.g., withpolymers, epoxies, metals, carbon (i.e., carbon/carbon materials) andhigh-T_(c) superconductors for flux pinning.

Macroscopic Carbon Fiber

The macroscopic carbon fiber produced as described herein is made up ofan aggregate of large number of single-wall nanotubes preferably ingenerally parallel orientation. While individual nanotubes may deviatefrom parallel orientation relative to any other individual nanotube,particularly for very short distances, over macroscopic distances theaverage orientation of all of the nanotubes preferably will be generallyparallel to that of all other nanotubes in the assembly (macroscopicdistances as described herein are generally considered to be greaterthan 1 micron). In one preferred form, the SWNTs will be arranged in aregular triangular lattice, i.e., in a closest packing relationship.

The carbon fiber of this invention is made up of individual tubularmolecules and may be in whole or in part either crystalline or amorphousin structure. The degree of order in the fiber will depend both on thegeometric relationship of the tubes in the molecular array and thegrowth and annealing conditions. The fiber may be subjected toorientation of other post-formation treatments before or aftercollection. The fiber produced by this process may, for example, befurther spun or braided into larger yarns or cables. It is alsocontemplated that as produced fiber will be large enough in diameter formany applications.

Generally, the macroscopic carbon fiber produced according to thisinvention consists of a sufficient number of substantially parallelsingle-wall nanotubes that it is large enough in diameter to bepractically handled as an individual fiber and/or processed into largercontinuous products. The macroscopic nature of the assembly of nanotubesis also important for end uses such as transmission of electric currentover these nanotube cables. A macroscopic carbon fiber according to thisinvention preferably will contain at least 10⁶ single-wall carbonnanotubes, and more preferably at least 10⁹ single-wall carbonnanotubes. The number of assembled nanotubes is vastly larger than thenumber (<10³) that spontaneously align during the formation ofsingle-wall nanotube ropes in the condensing carbon vapor of a carbonarc or laser vaporization apparatus. For many applications the preferreddiameter of the macroscopic carbon fiber of this invention will be inthe range of from about 1 to about 10 microns. Some applications, e.g.,power transmission cables, may require fiber diameters of up to a fewcentimeters. It is also possible to include dopants, e.g., metals,halogens, FeCl₃ and the like, physically entrapped between the tubes ofthe fiber.

The macroscopic carbon fiber of this invention will generally be atleast 1 millimeter in length, with the exact length depending upon theparticular application for which the fiber is used. For example, wherethe fiber is designed to substituted for conventional graphite carbonfiber for reinforcing, the length of the fiber according to thisinvention will be similar to the length of the convention carbon fibers.Where the macroscopic carbon fiber according to this invention is usedfor electrical conductance, the length of the fiber preferablycorresponds to the distance over which electrical conductance isdesired. Typically such distances may be from 1-100 microns or up to1-10 millimeters or greater. Where conductance over macroscopicdistances is desired, it is preferred that the macroscopic carbon fiberaccording to this invention have a length on the order of meters orgreater.

One reason the continuous carbon fiber of the present invention has suchimproved physical properties is its structure as a high orderlaminate—as many as 10⁹ or more individual tubular molecules arelaminated together. This structure provides much higher strength inbending, significantly higher resistance to failure by chemicalcorrosion, better wear, more elasticity and a completely differenttensile failure mechanism from similar monolithic materials. Thesingle-wall carbon nanotube fiber of this invention provides extremelyhigh tensile strength at low weight (˜100 times stronger than steelwhile having only one sixth the weight). This fiber has an electricalconductivity similar to copper. In addition the thermal conductivityalong the fiber is approximately that of diamond. The carbon fiber ofthis invention also has high chemical resistance (better than spheroidalfullerenes such as C⁶⁰-C⁷⁰). In general the substantially defect-freecontinuous carbon fiber of this invention will exhibit improvedproperties over conventional carbon fibers because of its near perfectmulti-hexagonal structure that extends over macroscopic distances.

In a particular embodiment, macroscopic carbon fiber according to thisinvention is grown from a molecular array comprising a SAM having aregion substantially comprising single-wall nanotubes in armchairorientation, the region having a diameter of at least one micron andpreferably at least 100 microns. By use of masks on the surface uponwhich the monolayer is assembled, the area containing single-wallednanotubes in armchair structure is completely surrounded on all sides bya concentric region of tubes having a chiral or zig-zag structure.Elongation from this template will produce a conducting core surroundedby a semi-conducting or insulating sheath, each layer made up of singlemolecules of essentially infinite length. In a similar manner, aco-axial transmission cable with several layers can be produced.

Applications of these carbon fibers include all those currentlyavailable for graphite fibers and high strength fibers such as membranesfor batteries and fuel cells; chemical filters; catalysts supports;hydrogen storage (both as an absorbent material and for use infabricating high pressure vessels); lithium ion batteries; and capacitormembranes. These fibers can also be used in electromechanical devicessuch as nanostrain gauges (sensitive to either nanotube bend or twist).Fibers of this invention can be used as product or spun into threads orformed into yarns or to fibers using known textile techniques.

The carbon fiber technology of this invention also facilitates a classof novel composites employing the hexaboronitride lattice. This materialforms graphene-like sheets with the hexagons made of B and N atoms(e.g., B₃ N₂ or C₂ BN₃). It is possible to provide an outer coating to agrowing carbon fiber by supplying a BN precursor (e.g.,tri-chloroborazine, a mixture of NH₃ and BCl₃ or diborane) to the fiberwhich serves as a mandrel for the deposition of BN sheets. This outer BNlayer can provide enhanced insulating properties to the metallic carbonfiber of the present invention. Outer layers of pyrolytic carbonpolymers or polymer blends may also be employed to impart. By changingthe feedstock in the above described process of this invention from ahydrocarbon to a BN precursor and back again it is possible to grow afiber made up of individual tubes that alternate between regions of allcarbon lattice and regions of BN lattice. In another embodiment of thisinvention, an all BN fiber can be grown by starting with a SWNT templatearray topped with a suitable catalyst and fed BN precursors. Thesegraphene and BN systems can be mixed because of the very close match ofsize to the two hexagonal units of structure. In addition, they exhibitenhanced properties due to the close match of coefficients of thermalexpansion and tensile properties. BN fibers can be used in composites asreinforcing and strengthening agents and many of the other usesdescribed above for carbon fibers.

Device Technology Enabled by Products of the Invention

The unique properties of the tubular carbon molecules, molecular arraysand macroscopic carbon fibers of the present invention provide excitingnew device fabrication opportunities.

1. Power Transmission Cable

Current power transmission-line designs generally employ aluminumconductors, often with steel strand cores for strength (i.e., theso-called ASCR conductor). The conductors have larger losses than copperconductors and generally are not shielded leading to corona dischargeproblems. The continuous carbon fibers made form large (>10⁶)aggregations of SWNTs can be used to fabricate power transmission cablesof unique designs and properties. One such design is shown in FIG. 10.This design is essentially a shielded coaxial cable capable of EHV(extra high voltage) power transmission, (i.e., >500 KV preferably over10⁶V) and having heretofore unattainable strength-to-weight propertiesand little or no corona discharge problems.

The illustrated design, which exemplifies the use of the SWNT-basedcarbon fiber conductors produced as described above (e.g., from n,nmetallic SWNTs), consists of a central conductor 30 and a coaxial outerconductor 31, separated by an insulating layer 32. The central conductorcarries the power transmission which the outer layer conductor is biasedto ground. The central conductor can be a solid metallic carbon fiber.Alternatively, the central conductor can comprise a bundle of metalliccarbon fiber strands which may be aggregated helically as is common inACSR conductors.

The inner conductor can also comprise an annular tube surrounding anopen core space in which the tube is a woven or braided fabric made frommetallic carbon fibers as described above. The insulating layer can beany light weight insulating material. Among the preferred embodimentsare strands or woven layers of BN fibers made as described above and theuse of an annular air space (formed using insulating spacers).

The outer conductor layer is also preferably made from hexically woundstrands of metallic carbon fiber as described above. This grounded layeressentially eliminates corona discharge problems or the need to takeconventional steps to reduce these emissions.

The resulting coaxial structure possesses extremely highstrength-to-weight properties and can be used to transmit greater thanconventional power levels over greater distances with lower losses.

One of the above described power cable assemblies can be used to replaceeach of the conductors used for separate phases in the conventionalpower transmission system. It is also possible by fabricating amultilayer annular cable with alternating metallic carbon fiberconductors and insulating layers to provide a single powertransmission-cable carrying three or more phases, thus greatlysimplifying the installation and maintenance of power lines.

2. Solar Cell

A Grätzel cell of the type described in U.S. Pat. No. 5,084,365(incorporated herein by reference in its entirety) can be fabricatedwith the nanocrystalline TiO₂ replaced by a monolayer molecular array ofshort carbon nanotube molecules as described above. The photoactive dyeneed not be employed since the light energy striking the tubes will beconverted into an oscillating electronic current which travels along thetube length. The ability to provide a large charge separation (thelength of the tubes in the array) creates a highly efficient cell. It isalso contemplated by the present invention to use a photoactive dye(such as cis-[bisthiacyanato bis(4,4′-dicarboxy-2,2′-bipyridine Ru(II))] attached to the end of each nanotube in the array to furtherenhance the efficiency of the cell. In another embodiment of the presentinvention, the TiO₂ nanostructure described by Grätzel can serve as anunderlying support for assembling an array of SWNT molecules. In thisembodiment, SWNTs are attached directly to the TiO₂ (by absorptiveforces) or first derivatized to provide a linking moiety and then boundto the TiO₂ surface. This structure can be used with or without aphotoactive dye as described above.

3. Memory Device

The endohedrally loaded tubular carbon molecule described above can beused to form the bit structure in a nanoscale bistable non-volatilememory device. In one form, this bit structure comprises a closedtubular carbon molecule with an enclosed molecular entity that can becaused to move back and forth in the tube under the influences ofexternal control. It is also possible to fill a short nanotube moleculewith magnetic nanoparticles (e.g., Ni/Co) to form a nanobit useful inmagnetic memory devices.

One preferred form of a bit structure is shown in FIG. 11. The tubularcarbon molecule 40 in this bit should be one that exhibits a good fitmechanically with the movable internal moiety 41, i.e., not too small toimpede its motion. The movable internal moiety should be chosen (1) tofacilitate the read/write system employed with the bit and (2) tocompliment the electronic structure of the tube.

One preferred arrangement of such a nanobit employs a short closedtubular carbon molecule (e.g., about 10-50 nm long) made from a (10,10)SWNT by the above-described process, and containing encapsulated thereina C₆₀ or C₇₀ spheroidal fullerene molecule. Optionally the C₆₀ or C₇₀molecule (bucky ball) can be endohedrally or exohedrally doped. The C₆₀bucky ball is almost a perfect fit in a (10,10) tube. More importantly,the electronic environment inside the tube is highly compatible withthat of the bucky ball, particularly at each end, since here the innercurvature of the (10,10) tube at the end cap matches the outer curvatureof the bucky ball. This configuration results in optimum van der Waalsinteraction. As shown in FIG. 12, the energy threshold required to getone bucky ball out of the end cap (where it is in the mostelectronically stable configuration) serves to render the bit bistable.

One preferred read/write structure for use with the memory bit describedabove is shown in FIG. 11. Writing to the bit is accomplished byapplying a polarized voltage pulse through a nanocircuit element 42(preferably a SWNT molecule). A positive pulse will pull the bucky balland a negative pulse will push the bucky ball. The bistable nature ofthe bit will result in the bucky ball staying in this end of the tubewhen the pulse is removed since that is where the energy is lowest. Toread the bit, another nanocircuit element 43 (again preferable, a SWNTmolecule) is biased with a V_(READ). If the bucky ball is present in thedetection end, it supplied the necessary energy levels for current toresonantly tunnel across the junction to the ground voltage 44 (in afashion analogous to a resonant tunneling diode) resulting in a firststable state being read. If the bucky ball is not present in thedetection end, the energy levels are shifted out of resonance and thecurrent does not tunnel across the junction and a second stable state isread. Other forms of read/write structure (e.g., microactuators) can beemployed as will be recognized by one skilled in the art.

A memory device can be constructed using either a two- orthree-dimensional array of the elements shown in FIG. 12. Because theelements of the memory array are so small (e.g., −5 nm×25 nm), extremelyhigh bit densities can be achieved, i.e., >1.0 terabit/cm² (i.e., a bitseparation of 7.5 nm). Because the bucky ball only has to move a fewnanometers and its mass is so small, the write time of the describeddevice is on the order of 10⁻¹⁰ seconds.

4 Lithium Ion Battery

The present invention also relates to a lithium ion secondary battery inwhich the anode material includes a molecular array of SWNTs made asdescribed above (e.g., by SAM techniques). The anode material cancomprise a large number (e.g., >10³) short nanotube molecules bound to asubstrate. Alternatively, the end of a macroscopic carbon fiber asdescribed above can serve as the microporous anode surface.

The tubular carbon molecules in this array may be open or closed. Ineither case, each tubular carbon molecule provides a structurally stablemicroporosity for the intercalation of lithium ions, i.e., into the opentubes or into triangular pores of an end cap. The resulting fullereneintercalation compound (FIC) can be used, for example, with an aproticorganic electrolyte containing lithium ions and a LiCoO₂ cathode to forman improved lithium ion secondary battery of the type described inNishi, “The Development of Lithium Ion Secondary Batteries,” 1996 IEEEsymposium on VLSI Circuits and shown in FIG. 13. In this figure, theanode 50 comprises a large number of SWNTs 51 in an ordered moleculararray. Cathode 52, electrolyte 53, lithium ions 54 and electrons 55 makeup the remaining elements of the cell.

The use of the molecular array FICs of this invention provides alithium-storing medium that has a high charge capacity (i.e., >600 mAh/g) which is stable during charging and possesses excellent cylabilityand that results in an improved safe rechargeable battery.

The anode is characterized by high current, high capacity, lowresistance, highly reversible and is nano-engineered from carbon withmolecular perfection. The anode is constructed as a membrane of metallicfullerene nanotubes arrayed as a bed-of-nails, the lithium atoms beingstored in the spaces either between the adjacent tubes or down thehollow pore within each tube. Chemical derivatization of the open endsof the tubes will then be optimized to produce the best possibleinterface with the electrolyte. The derivative is preferably an organicmoiety which provides a stable interface where the redox reaction canoccur. In general, the organic moiety should be similar in structure tothe electrolyte. One preferred derivitizing agent is polyethylene oxideand, in particular, polyethylene oxide oligomers.

The electrochemistry of the nano-engineered nanotube membranes are usedfor electrode applications. Important aspects are to derivatize theirends and sides in such a way as to provide an optimal interface for alithium-ion battery electrolyte. This will result in a battery electrodethat is highly accessible to the lithium ions, therefore capable ofdelivering high power density, and equally important, overcomes theubiquitous SEI (solid-electrolyte interface) problem that significantlyreduces electrode capacity and reversibility.

Li⁺ is the ion choice for rechargeable batteries. Bested only by theproton as a lightweight counter-ion, Li profits from the availability ofa wide class of solid and liquid electrolytes as a large choice ofcathode materials, primarily metal oxides with 3D networks ofintercalation sites in which the Li⁺ resides in the discharged state.The first rechargeable Li batteries used metallic Li as an anode butseveral drawbacks existed:

loss of Li due to dendrite growth during recharging;

safety problems associated with the reactivity of Li metal in thepresence of organic solvents; and

the potential for anode-cathode shorts through the separator due to theaforementioned Li dendrites.

A solution to the safety problems was found by replacing Li metal by aLi-carbon intercalation anode, giving birth to the “rocking chair”battery in which the Li is never reduced to Li⁰ and Li⁺ shuttles betweenintercalation sites in the carbon anode and metal cathode as the batteryis charged and discharged respectively. Graphite was used in the firstgeneration Li-ion batteries, largely because the solid state chemistryof Li-graphite was well understood. Happily, the potential of Li⁺ ingraphite is within a few tens of MV of the potential of Li⁰, so the useof graphite in place of Li metal imposes a small weight and volumepenalty but no significant penalty in cell voltage.

But the use of graphite brought its own problems to the technology:

the best electrolytes (e.g., LiClO₄ dissolved in propylene carbonate)which have good Li⁺ conductivity at ambient T also co-intercalate bysolving the Li⁺, leaving to exfoliation of the graphite, dimensionalinstabilities and premature failure, and

the diffusivity of Li⁺ in graphite is rather low at ambient T,controlled by the large barrier for jump diffusion (commensuratelattice) between adjacent hexagonal interstitial sites in the graphitelattice.

The first problem was overcome by the development of new electrolytewhich did not co-intercalate, e.g., LiPF₆ in a mixture of dimethylcarbonate and ethylene carbonate, which however had a detrimental effecton the electrolyte contribution to ion transport kinetics. The secondprolem required the use of finely divide graphite (powder, choppedfibers, foams) which in turn increased the surface area substantially,leading inexorably to yet a new set of problems, namely capacity fadedue to the formation of surface film (SEI: “solid-electrolyteinterphase”) during the first anode intercalation half-cycle. This inturn required assembling the battery with extra Li-containing cathodematerial to provide for the Li consumed by SEI formation, thus reducingthe capacity. Not much is known about the SEI, but it is widely agreedthat the carbonates (from electrolyte decomposition) are an importantconstituent. A widely accepted criterion in industry is that capacityloss due to SEI formation should not exceed 10% of the available Li.

Subsequent research explored the use of other forms of(nano-crystalline) carbon: carbon black, pyrolyzed coal and petroleumpitches and polymers, pyrolyzed natural products (sugars, nutshells,etc.), “alloys” of carbon with other elements (boron, silicon, oxygen,hydrogen), and entirely new systems such as tin oxides. Some of theseexhibit much lager Li capacities than graphite, but the microscopicorigins of this “excess capacity” are largely unknown. In general thecycling behavior of these materials is much worse than graphite, and thehydrogen-containing materials also exhibit large hysteresis in cellpotential vs. Li concentration between charge and discharge half-cycles,a very undesirable property for a battery. Again, the origin of thehysteresis is largely unknown. The main advantage of these materials isthat their inherently finely-divided nature augurs well for fastkinetics, an absolute prerequisite if LIB's are to have an impact inhigh current applications (e.g., electric vehicle).

The anode of the present invention is entirely nano-fabricated withmolecular precision. It has a large capacity per unit volume to storelithium at an electrochemical potential near that of lithium metal, andis protected from the dendrite growth problems and safety concerns thatplague pure metal anodes. It has extremely fast kinetics for chargingand discharging, but maintains its architectural and chemical integrityin at all states of charge and discharge. In addition, there is a meansfor custom designing the interface between this anode and theelectrolyte such that the Li⁰⇄Li⁺¹ redox chemistry is highly reversibleand very low in effective resistance.

A design for such an anode is one which consists of an array offullerene nanotubes, attached to a metallic support electrode, such asgold-coated copper, and arranged in a hexagonal lattice much like a bedof nails. As shown in FIG. 14, this structure has the virtue that thestorage area for the reduced state of the lithium, Li⁰, is down deepchannels either between the nanotubes or down the hollow core of thetubes themselves. Accordingly, the redox chemistry of the lithium isconfined primarily to the exposed ends of the nanotubes, and herederivatization of the nanotube ends provides great opportunities toinsure that this redox chemistry is as reversible as possible.

5. Three-Dimensional Self-Assembling SWNT Structures

The self-assembling structures contemplated by this invention arethree-dimensional structures of derivatized SWNT molecules thatspontaneously form when the component molecules are brought together. Inone embodiment the SAM, or two-dimensional monolayer, described abovemay be the starting template for preparing a three dimensionalself-assembling structures. Where the end caps of the component SWNTmolecules have mono-functional derivatives the three-dimensionalstructure will tend to assemble in linear head-to-tail fashion. Byemploying multi-functional derivatives or multiple derivatives atseparate locations it is possible to create both symmetrical and nonsymmetrical structures that are truly three-dimensional.

Carbon nanotubes in material obtained according to the foregoing methodsmay be modified by ionically or covalently bonding functionally-specificagents (FSAs) to the nanotube. The FSAs may be attached at any point orset of points on the fullerene molecule. The FSA enables self-assemblyof groups of nanotubes into geometric structures. The groups may containtubes of differing lengths and use different FSAs. Self-assembly canalso occur as a result of van der waals attractions between derivitizedor underivitized or a combination of derivitized and underivitizedfullerene molecules. The bond selectivity of FSAs allow selectednanotubes of a particular size or kind to assemble together and inhibitthe assembling of unselected nanotubes that may also be present. Thus,in one embodiment, the choice of FSA may be according to tube length.Further, these FSAs can allow the assembling of two or more carbonnanotubes in a specific orientation with respect to each other.

By using FSAs on the carbon nanotubes and/or derivitized carbonnanotubes to control the orientation and sizes of nanotubes which areassembled together, a specific three-dimensional structure can be builtup from the nanotube units. The control provided by the FSAs over thethree-dimensional geometry of the self assembled nanotube structure canallow the synthesis of unique three-dimensional nanotube materialshaving useful mechanical, electrical, chemical and optical properties.The properties are selectively determined by the FSA and the interactionof and among FSAs.

Properties of the self-assembled structure can also be affected bychemical or physical alteration of the structure after assembly or bymechanical, chemical, electrical, optical, and/or biological treatmentof the self-assembled fullerene structure. For example, other moleculescan be ionically or covalently attached to the fullerene structure orFSAs could be removed after assembly or the structure could berearranged by, for example, biological or optical treatment. Suchalterations and/or modifications could alter or enable electrical,mechanical, electromagnetic or chemical function of the structure, orthe structure's communication or interaction with other devices andstructures.

Examples of useful electric properties of such a self-assembledgeometric structure include: operation as an electrical circuit, aspecific conductivity tensor, a specific response to electromagneticradiation, a diode junction, a 3-terminal memory device that providescontrollable flow of current, a capacitor forming a memory element, acapacitor, an inductor, a pass element, or a switch.

The geometric structure may also have electromagnetic properties thatinclude converting electromagnetic energy to electrical current, anantenna, an array of antennae, an array that produces coherentinterference of electromagnetic waves to disperse those of differentwavelength, an array that selectively modifies the propagation ofelectromagnetic waves, or an element that interacts with optical fiber.The electromagnetic property can be selectively determined by the FSAand the interaction of and among FSAs. For example, the lengths,location, and orientation of the molecules can be determined by FSAs sothat an electromagnetic field in the vicinity of the molecules induceselectrical currents with some known phase relationship within two ormore molecules. The spatial, angular and frequency distribution of theelectromagnetic field determines the response of the currents within themolecules. The currents induced within the molecules bear a phaserelationship determined by the geometry of the array. In addition,application of the FSAs could be used to facilitate interaction betweenindividual tubes or groups of tubes and other entities, whichinteraction provides any form of communication of stress, strain,electrical signals, electrical currents, or electromagnetic interaction.This interaction provides an “interface” between the self-assemblednanostructure and other known useful devices.

Choice of FSAs can also enable self-assembly of compositions whosegeometry imparts useful chemical or electrochemical properties includingoperation as a catalyst for chemical or electrochemical reactions,sorption of specific chemicals, or resistance to attack by specificchemicals, energy storage or resistance to corrosion.

Examples of biological properties of FSA self-assembled geometriccompositions include operation as a catalyst for biochemical reactions;sorption or reaction site specific biological chemicals, agents orstructures; service as a pharmaceutical or therapeutic substance;interaction with living tissue or lack of interaction with livingtissue; or as an agent for enabling any form of growth of biologicalsystems as an agent for interaction with electrical, chemical, physicalor optical functions of any known biological systems.

FSA assembled geometric structures can also have useful mechanicalproperties which include but are not limited to a high elastic tomodulus weight ratio or a specific elastic stress tensor. Opticalproperties of geometric structures can include a specific opticalabsorption spectrum, a specific optical transmission spectrum, aspecific optical reflection characteristic, or a capability formodifying the polarization of light.

Self-assembled structures, or fullerene molecules, alone or incooperation with one another (the collective set of alternatives will bereferred to as “molecule/structure”) can be used to create devices withuseful properties. For example, the molecule/structure can be attachedby physical, chemical, electrostatic, or magnetic means to anotherstructure causing a communication of information by physical, chemical,electrical, optical or biological means between the molecule/structureand other structure to which the molecule/structure is attached orbetween entities in the vicinity of the molecule/structure. Examplesinclude, but are not limited to, physical communication via magneticinteraction, chemical communication via action of electrolytes ortransmission of chemical agents through a solution, electricalcommunication via transfer of electronic charge, optical communicationvia interaction with and passage of any form with biological agentsbetween the molecule/structure and another entity with which thoseagents interact.

6. SWNT Antenna

Fullerene nanotubes can be used to replace the more traditionalconductive elements of an antenna. For example, an (n,n) tube inconjunction with other materials can be used to form a Schottky barrierwhich would act as a light harvesting antenna. In one embodiment, a(10,10) tube can be connected via sulfur linkages to gold at one end ofthe tube and lithium at the other end of the tube forming a naturalSchottky barrier. Current is generated through photo conductivity. Asthe (10,10) tube acts like an antenna, it pumps electrons into oneelectrode, but back flow of electrons is prevented by the intrinsicrectifying diode nature of the nanotube/metal contact.

In forming an antenna, the length of the nanotube can be varied toachieve any desired resultant electrical length. The length of themolecule is chosen so that the current flowing within the moleculeinteracts with an electromagnetic field within the vicinity of themolecule, transferring energy from that electromagnetic field toelectrical current in the molecule to energy in the electromagneticfield. This electrical length can be chosen to maximize the currentinduced in the antenna circuit for any desired frequency range. Or, theelectrical length of an antenna element can be chosen to maximize thevoltage in the antenna circuit for a desired frequency range.Additionally, a compromise between maximum current and maximum voltagecan be designed.

A Fullerene nanotube antenna can also serve as the load for a circuit.The current to the antenna can be varied to produce desired electric andmagnetic fields. The length of the nanotube can be varied to providedesired propagation characteristics. Also, the diameter of the antennaelements can be varied by combining strands of nanotubes.

Further, these individual nanotube antenna elements can be combined toform an antenna array. The lengths, location, and orientation of themolecules are chosen so that electrical currents within two or more ofthe molecules act coherently with some known phase relationship,producing or altering an electromagnetic field in the vicinity of themolecules. This coherent interaction of the currents within themolecules acts to define, alter, control, or select the spatial, angularand frequency distributions of the electromagnetic field intensityproduced by the action of these currents flowing in the molecules. Inanother embodiment, the currents induced within the molecules bear aphase relationship determined by the geometry of the array, and thesecurrents themselves produce a secondary electromagnetic field, which isradiated from the array, having a spatial, angular and frequencydistribution that is determined by the geometry of the array and itselements. One method of forming antenna arrays is the self-assemblymonolayer techniques discussed above.

7. Fullerene Molecular Electronics

Fullerene molecules can be used to replace traditional electricallyconducting elements. Thus fullerene molecules or self-assembledfullerene groups can be the basis of electrical circuits in which themolecule transfers electrical charge between functional elements of thecircuit which alter or control the flow of that charge or objects inwhich the flow of electrical current within the object performs someuseful function such as the redistribution of the electric field aroundthe object or the electric contact in a switch or a response of theobject to electromagnetic waves.

As an example, nanotubes can also be self-assembled to form a bridgecircuit to provide full wave rectification. This device can include fournanotubes, each forming an edge of a square, and four buckyballs, onebuckyball would be located at each corner of the square. The buckyballsand nanotubes can be derivitized to include functionally specificagents. The functionally specific agents form linkages connecting thebuckyballs to the nanotubes and imparting the required geometry of thebridge.

A fullerene diode can be constructed through the self-assemblytechniques described above. The diode can be composed of two bucky tubesand a bucky capsule. The bucky capsule can also be derivitized to form azwiterrion. For example, the bucky capsule can include two positivegroups, such as the triethyl amine cation and two negative groups, suchas CO₂-anion. In one embodiment, each end of the bucky capsule isconnected to a (10,10) bucky tube by a disulfide bridge. Thus, sulfurserves as the functionally-specific agent.

8. Probes and Manipulators

The SWNT molecules of the present invention also enable the fabricationof probes and manipulators on a nanoscale. Probe tips for AFM and STMequipment and AFM cantilevers are examples of such devices. Derivatizedprobes can serve as sensors or sensor arrays that effect selectivebinding to substrates. Devices such as these can be employed for rapidmolecular-level screening assays for pharmaceuticals and other bioactivematerials. Further, conducting SWNT molecules of the present inventionmay also be employed as an electrochemical probe.

Similarity probe-like assemblies of SWNT molecules can be used with orwithout derivatives as tools to effect material handling and fabricationof nanoscale device, e.g., nanoforcepts. In addition, these moleculartools can be used to fabricate MEMS (Micro Electro Mechanical Systems)and also can be employed as connecting elements or circuit elements inNANO-MEMS.

9. Composite Materials Containing Carbon Nanotubes

Composite materials, i.e., materials that are composed of two or morediscrete constituents, are known. Typically, composites include amatrix, which serves to enclose the composite and give it its bulk form,and a structural constituent, which determines the internal structure ofthe component. The matrix deforms and distributes an applied stress tothe structural constituent.

Although composites are generally extremely strong, their strength isgenerally anisotropic, being much less in the direction perpendicular tothe plane of the composite material than any parallel direction. Becauseof this characteristic, composites that are formed in layers or inlaminate strips are prone to delamination. Delamination may occur whenat least one layer of the composite separates from the others, resultingin a void in the bulk of the composite material. This void isexceedingly difficult to detect, and with repeated applications ofstress to the composite element, the composite element will failcatastrophically, without warning.

Carbon nanotubes may serve as structural constituents in compositematerials. As discussed above, composite materials are generallycomposed of two or more discrete constituents, usually including amatrix, which gives the composite its bulk form, and at least onestructural constituent, which determines the internal structure of thecomposite. Matrix materials useful in the present invention can includeany of the known matrix materials presently employed (see e.g., Mel M.Schwartz, Composite Materials Handbook (2d ed. 1992)). Among those knownmatrix materials are resins (polymers), both thermosetting andthermoplastic, metals, ceramics, and cermets.

Thermosetting resins useful as matrix materials include phthalic/maelictype polyesters, vinyl esters, epoxies, phenolics, cyanates,bismaleimides, and nadic end-capped polyimides (e.g., PMR-15).Thermoplastic resins include polysulfones, polyamides, polycarbonates,polyphenylene oxides, polysulfides, polyether ether ketones, polyethersulfones, polyamide-imides, polyetherimides, polyimides, polyarylates,and liquid crystalline polyester. In a preferred embodiment, epoxies areused as the matrix material.

Metals useful as matrix materials include alloys of aluminum such asaluminum 6061, 2024, and 713 aluminum braze. Ceramics useful as matrixmaterials include glass ceramics, such as lithium aluminosilicate,oxides such as alumina and mullite, nitrides such as silicon nitride,and carbides such a silicon carbide. Cermets useful as matrix materialsinclude carbide-base cermets (tungsten carbide, chromium carbide, andtitanium carbide), refractory cements (tungsten-thoria andbarium-carbonate-nickel), chromium-alumina, nickel-magnesia, andiron-zirconium carbide.

The carbon nanotube structural constituent according to the presentinvention can take any of the forms described herein and known in theart. Preferably, a fullerene nanotube, i.e., a carbon nanotube withmolecular perfection, is used. Fullerene nanotubes are made of a single,continuous sheet of hexagonal graphene joined perfectly to form a tubewith a hemifullerene cap at either end. It may be either a truesingle-walled fullerene tube itself with hemispherical caps attached, orit may refer to one derived from such a closed tube by cutting, etchingoff the ends, etc. Alternatively, it is a multi-walled fullerenenanotube constructed of some number of single-walled fullerene nanotubesarranged one inside another. Arc-grown multi-walled nanotubes (MWNT),though approaching the fullerene ideal, are still not perfect. They havesignificant structural defects of lesions at least every 100 nm or so ormore in their multiple walls. The single-walled carbon nanotubes made bythe laser/oven method, however, appear to be molecularly perfect. Theyare fullerene nanotubes, and fibers made from them are true fullerenefibers.

The single-wall fullerene nanotubes may be metallic (formed in thearmchair or (n,n) configuration) or any other helicity configuration.The nanotubes may be used in the form of short individual tubularmolecules cut to any appropriate length. Cut nanotubes have theheretofore unachievable advantage of providing strengthening andreinforcement on a molecular scale. As they approach the micron scale inlength, however, they become very flexible while still retaining therigid tubular properties on a molecular scale.

Aggregates of individual tubes referred to herein as ropes having up toabout 10³ carbon nanotubes may also be employed. Ropes of carbonnanotubes produced as described above have the advantage of anentangled, loopy physical configuration on a micron scale that resultsin a Velcro-like interaction with each other and matrix material whilestill retaining the rigid tubular bundle structure on a molecular level.

Macroscopic carbon nanotube fibers (having at least 10⁶ individualtubes), in either the continuous or random fiber forms described above,can also be employed to form the composite of the present invention.Ropes and fibers may be cut into desired lengths as described herein orused as tangled, loopy felts or the like.

The present invention also contemplates composites in which carbonnanotubes are present in two or more of the foregoing forms, e.g., mixedin the same matrix area or having different nanotube forms in differentareas of the matrix. Selection of the carbon nanotube form will dependon the nature of the composite and its desired final properties. Thecarbon nanotubes are preferably cleaned and purified as described hereinbefore use.

The nanotubes, ropes, or fibers used in the composites may also bederivatized as described above. End cap derivatization of carbonnanotubes can facilitate the bonding of the carbon nanotubes to eachother or to the matrix material. While pure carbon nanotubes generallycontain side walls that are entirely uniform (consisting of an array ofthe hexagonal carbon lattice similar to that of graphite), it ispossible to introduce defects or create bonding sites in the sidewallsto facilitate bonding adhesion to the matrix material. One example wouldbe to incorporate an impurity such as Boron atoms in the side wall. Thewall defect or bonding site thus created may facilitate interaction ofthe nanotube with the matrix material through physical or chemicalforces. It is additionally possible that such defect or bonding site mayfacilitate chemical reactions between the tube itself and the matrixmaterial in a way that affects the properties of the composite materialformed. As described above, the carbon nanotube material may also have apart of its lattice replaced with boron nitride.

Other fibrous structural constituents, both organic and inorganic, mayalso be used in conjunction with the carbon nanotube materials of thisinvention. Examples of organic constituents that may be used includecellulose. Examples of inorganic constituents include carbon, glass (D,E, and S-type), graphite, silicon oxide, carbon steel, aluminum oxide,beryllium, beryllium oxide, boron, boron carbide, boron nitride,chromium, copper, iron, nickel, silicon carbide, silicon nitride, FPalumina yarn manufactured by DuPont, Nextel alumina-boria-silica andzirconia-silica manufactured by 3M, Saffil HT zircona and aluminamanufacture by ICI, quartz, molybdenum, René 41, stainless steel,titanium boride, tungsten, and zirconium oxide.

Fabrication of the composite of the present invention can employ any ofthe well-known techniques for combining the matrix material with thestructural constituent. Carbon nanotubes, as individual tubularmolecules or as ropes, can be dispersed in a liquid carrier, e.g., wateror organic solvents, to facilitate incorporation into a matrix material.Macroscopic carbon nanotube fibers can be handled in the conventionalmanner employed in the current processes using carbon or graphitefibers.

The carbon nanotube structural constituent may be uniformly mixed with amatrix material precursor (polymer solution, pre-fired ceramic particlesor the like) and then converted to a composite by conventionaltechniques. Structural layers or components (e.g., felts or bucky paper)can also be preformed from the carbon nanotube materials and impregnatedwith a prepolymer solution to form the composite.

The carbon nanotube structural constituents may also be used to improvethe properties of conventional composite materials. One such exampleinvolves composites built-up of fibrous laminates impregnated and bondedwith a polymer matrix material. Graphite fiber fabric layers bonded withan epoxy system is a well-known example of such a composite. By usingcarbon nanotube ropes or fibers that exhibit a 3-D loopy structure addedonly at the epoxy/graphite interfaces, resistance to delamination of theresulting laminar composite can be substantially increased. The carbonnanotube material can be dispersed in the epoxy system beforeimpregnation (or premixed into one of the reactive components thereof).The carbon nanotube material can also be dispersed in a liquid carrierand sprayed or otherwise applied to the laminate as each graphite fabriclayer is added.

A single-walled fullerene nanotube such as the (10,10) tube is unique asa component in a composite. From one perspective, it is simply a newmolecular polymer, like polypropylene, Nylon, Kevlar, or DNA. It isabout the diameter of the DNA double-helix, but vastly stiffer inbending and stronger in tension. Long chain polymers are characterizedby their persistence length (the distance one has to travel along thelength before there is a substantial change in the chain direction underconditions of normal Brownian motion). For polypropylene, this distanceis only about 1 nm, and for the DNA double-helix it is about 50 nm. Butfor a single (10,10) fullerene nanotube, it is greater than 1000 nm. Soon the persistence length scale of normal polymer molecules such asthose that would constitute the continuous phase of a compositematerial, fullerene nanotubes are effectively rigid pipes.

Yet on the length scale of a micron or so, a single (10,10) fullerenenanotube is a highly flexible tube, easily becoming involved with othernanotubes in tangles with many loops. These tangles and loops providetwo new opportunities in the internal mechanics of composites: (1) thecontinuous phase can interpenetrate through these loops, resulting inthe nanotubes being intimately “tied” to this phase on a sub-micronlength scale, and (2) with processing by flow and shear of the compositemixture before it sets up, the loops can become entangled in one anotherand pulled taught. As a result, composites made of fullerene tangleshave extra toughness, strength, and resistance to delamination failure.

Fullerenes like C₆₀ or C₇₀ are known to be effectively sponges for freeradicals. Similarly, fullerene nanotubes such as the (10,10) tube willchemisorb free radicals like methyl, phenyl, methoxy, phenoxy, hydroxy,etc., to their sides. As with the smaller fullerenes, these chemisorbedspecies do not substantially weaken the cage network (dissociation athigh temperatures simply desorbes the surface species, maintaining thefullerene structure intact). Accordingly, in a composite containingfullerene nanotubes, one can achieve a covalent coupling to thecontinuous polymer phase simply by attaching pendant groups on thepolymer which produces a free radical upon heating or photolysis withultraviolet light. The azo-linkage, as found in azo-bis-isobutylnitrile,for example, is quite effective as a photo-activated free radicalsource.

The unique properties of the carbon fiber produced by the presentinvention also permit new types of composite reinforcement. It ispossible, for example, to produce a composite fiber/polymer withanisotropic properties. This can, for example, be accomplished bydispersing a number of metallic carbon nanotube fibers (e.g., from (n,n)SWNTs) in a prepolymer solution (e.g., a poly methymethacrylate) andusing an external electric field to align the fibers, followed bypolymerization. Electrically conductive components can also be formedusing the metallic forms of carbon nanotubes.

Applications of these carbon nanotubes containing composites include,but are not limited to, all those currently available for graphitefibers and high strength fibers such as Kevlar, including: structuralsupport and body panels and for vehicles, including automobiles, trucks,and trains; tires; aircraft components, including airframes,stabilizers, wing skins, rudders, flaps, helicopter rotor blades,rudders, elevators, ailerons, spoilers, access doors, engine pods, andfuselage sections; spacecraft, including rockets, space ships, andsatellites; rocket nozzles; marine applications, including hullstructures for boats, hovercrafts, hydrofoils, sonar domes, antennas,floats, buoys, masts, spars, deckhouses, fairings, and tanks; sportinggoods, including golf carts, golf club shafts, surf boards, hang-gliderframes, javelins, hockey sticks, sailplanes, sailboards, ski poles,playground equipment, fishing rods, snow and water skis, bows, arrows,racquets, pole-vaulting poles, skateboards, bats, helmets, bicycleframes, canoes, catamarans, oars, paddles, and other items;mass-produced modular homes; mobile homes; windmills; audio speakers;furniture, including chairs, lamps, tables, and other modern furnituredesigns; soundboards for string instruments; lightweight armoredproducts for personnel, vehicle, and equipment protection; appliances,including refrigerators, vacuum cleaners, and air conditioners; tools,including hammer handles, ladders, and the like; biocompatible implants;artificial bones; prostheses; electrical circuit boards; and pipes ofall kinds.

EXAMPLES

In order to facilitate a more complete understanding of the invention, anumber of Examples are provided below. However, the scope of theinvention is not limited to specific embodiments disclosed in theseExamples, which are for purposes of illustration only.

Example 1 Oven Laser-Vaporization

The oven laser-vaporization apparatus described in FIG. 1 and alsodescribed by Haufler et al., “Carbon Arc Generation of C₆₀ ,” Mat. Res.Soc. Symp. Proc., Vol. 206, p. 627 (1991) and by U.S. Pat. No. 5,300,203was utilized. An Nd:YAG laser was used to produce a scanning laser beamcontrolled by a motor-driven total reflector that was focused to a 6 to7 mm diameter spot onto a metal-graphite composite target mounted in aquartz tube. The laser beam scans across the target's surface undercomputer control to maintain a smooth, uniform face on the target. Thelaser was set to deliver a 0.532 micron wavelength pulsed beam at 300milliJoules per pulse. The pulse rate was 10 hertz and the pulseduration was 10 nanoseconds (ns).

The target was supported by graphite poles in a 1-inch quartz tubeinitially evacuated to 10 m Torr. and then filled with 500 Torr. argonflowing at 50 standard cubic centimeters per second (sccm). Given thediameter of the quartz tube, this volumetric flow results in a linearflow velocity through the quartz tube in the range of 0.5 to 10 cm/sec.The quartz tube was mounted in a high-temperature furnace with a maximumtemperature setting of 1200° C. The high-temperature furnace used was aLindberg furnace 12 inches long and was maintained at approximately1000° to 1200° C. for the several experiments in Example 1. The laservaporized material from the target and that vaporized material was sweptby the flowing argon gas from the area of the target where it wasvaporized and subsequently deposited onto a water-cooled collector, madefrom copper, that was positioned downstream just outside the furnace.

Targets were uniformly mixed composite rods made by the followingthree-step procedure: (i) the paste produced from mixing high-puritymetals or metal oxides at the ratios given below with graphite powdersupplied by Carbone of America and carbon cement supplied by Dylon atroom temperature was placed in a 0.5 inch diameter cylindrical mold,(ii) the mold containing the paste was placed in a hydraulic pressequipped with heating plates, supplied by Carvey, and baked at 130° C.for 4 to 5 hours under constant pressure, and (iii) the baked rod(formed from the cylindrical mold) was then cured at 810° C. for 8 hoursunder an atmosphere of flowing argon. For each test, fresh targets wereheated at 1200° C. under flowing argon for varying lengths of time,typically 12 hours, and subsequent runs with the same targets proceededafter 2 additional hours heating at 1200° C.

The following metal concentrations were used in this example. cobalt(1.0 atom per cent), copper (0.6 atom per cent), niobium (0.6 atom percent), nickel (0.6 atom per cent), platinum (0.2 atom per cent), amixture of cobalt and nickel (0.6 atom per cent/0.6 atom per centrespectively), a mixture of cobalt and platinum (0.6 atom per cent/0.2atom per cent respectively), a mixture of cobalt and copper (0.6 atomper cent/0.5 atom per cent respectively), and a mixture of nickel andplatinum (0.6 atom per cent/0.2 atom per cent respectively). Theremainder of the mixture was primarily graphite along with small amountsof carbon cement. Each target was vaporized with a laser beam and thesoots collected from the water cooled collector were then collectedseparately and processed by sonicating the soot for 1 hour in a solutionof methanol at room temperature and pressure (other useful solventsinclude acetone, 1,2-dicholoroethane, 1-bromo, 1,2-dichloroethane, andN,N-dimethylformamide). With one exception, the products collectedproduced a homogeneous suspension after 30 to 60 minutes of sonicationin methanol. One sample vaporized from a mixture of cobalt, nickel andgraphite was a rubbery deposit having a small portion that did not fullydisperse even after 2 hours of sonication in methanol. The soots werethen examined using a transmission electron microscope with a beamenergy of 100 keV (Model JEOL 2010).

Rods (0.5 inch diameter) having the Group VIII transition metal ormixture of two VIII transition metals described above were evaluated inthe experimental apparatus to determine the yield and quality ofsingle-wall carbon nanotubes produce. No multi-wall carbon nanotubeswere observed in the reaction products. Yields always increased withincreasing oven temperature up to the limit of the oven used (1200° C.).At 1200° C. oven temperature, of the single metals utilized in theexample, nickel produced the greatest yield of single-wall carbonnanotubes followed by cobalt. Platinum yielded a small number ofsingle-wall carbon nanotubes and no single-wall carbon nanotubes wereobserved when carbon was combined only with copper or only with niobium.With respect to the mixtures of two Group VIII transition metalcatalysts with graphite, the cobalt/nickel mixture and thecobalt/platinum mixtures were both approximately equivalent and bothwere the best overall catalysts in terms of producing yields ofsingle-wall carbon nanotubes. The yield of single-wall carbon nanotubesfor both of these two metal mixtures were 10 to 100 times the yieldobserved when only one Group VIII transition metal was used. The mixtureof nickel and platinum with graphite also had a higher yield ofsingle-wall carbon nanotubes than a single metal alone. Thecobalt/copper mixture with graphite produced a small quantity ofsingle-wall carbon nanotubes.

The cobalt/nickel mixture with graphite and the cobalt/platinum mixturewith graphite both produced deposits on the water cooled collector thatresembled a sheet of rubbery material. The deposits were removed intact.The cobalt/platinum mixture produced single-wall carbon nanotubes in ayield estimated at 15 weight per cent of all of the carbon vaporizedfrom the target. The cobalt/nickel mixture produced single-wall carbonnanotubes at yields of over 50 wt % of the amount of carbon vaporized.

The images shown in FIGS. 15A through 15E are transmission electronmicrographs of single-wall carbon nanotubes produced by vaporizing atarget comprising graphite and a mixture of cobalt and nickel (0.6 atomper cent/0.6 atom per cent respectively) at an oven temperature of 1200°C. FIG. 15A shows a medium-magnification view (where the scale barrepresents 100 mm) showing that almost everywhere, bundles ofsingle-wall carbon nanotubes are tangled together with other single-wallcarbon nanotubes. FIG. 15B is a high-magnification image of one bundleof multiple single-wall carbon nanotubes that are all roughly parallelto each other. The single-wall carbon nanotubes all have a diameter ofabout 1 nm, with similar spacing between adjacent single-wall carbonnanotubes. The single-wall carbon nanotubes adhere to one another by vander Waals forces.

FIG. 15C shows several overlapping bundles of single-wall carbonnanotubes, again showing the generally parallel nature of eachsingle-wall nanotube with other single-wall carbon nanotubes in the samebundle, and showing the overlapping and bending nature of the variousbundles of single-wall carbon nanotubes. FIG. 15D shows severaldifferent bundles of single-wall carbon nanotubes, all of which are bentat various angles or arcs. One of the bends in the bundles is relativelysharp, illustrating the strength and flexibility of the bundle ofsingle-wall carbon nanotubes. FIG. 15E shows a cross-sectional view of abundle of 7 single-wall carbon nanotubes, each running roughly parallelto the others. All of the transmission electron micrographs in FIGS. 15Athrough 10E clearly illustrate the lack of amorphous carbon overcoatingthat is typically seen in carbon nanotubes and single-wall carbonnanotubes grown in arc-discharge methods. The images in FIGS. 15Athrough 15E also reveal that the vast majority of the deposit comprisessingle-wall carbon nanotubes. The yield of single-wall carbon nanotubesis estimated to be about 50% of the carbon vaporized. The remaining 50%consists primarily of fullerenes, multi-layer fullerenes (fullereneonions) and/or amorphous carbon.

FIGS. 15A through 15E show transmission electron microscope images ofthe products of the cobalt/nickel catalyzed carbon nanotube materialthat was deposited on the water cooled collector in the laservaporization apparatus depicted in FIG. 1. Single-wall carbon nanotubeswere typically found grouped in bundles in which many tubes ran togetherroughly parallel in van der Waals contact over most of their length. Thegrouping resembled an “highway” structure in which the bundles ofsingle-wall carbon nanotubes randomly criss-crossed each other. Theimages shown in FIGS. 15A through 15E make it likely that a very highdensity of single-wall carbon nanotubes existed in the gas phase inorder to produce so many tubes aligned as shown when landing on the coldwater cooled collector. There also appeared to be very little othercarbon available to coat the single-wall carbon nanotubes prior to theirlanding on the water cooled collector in the alignment shown. Evidencethat single-wall carbon nanotubes grow in the gas phase, as opposed tofor example on the walls of the quartz tube, was provided in earlierwork on multi-walled carbon nanotubes using the same method. See Guo etal., “Self-Assembly of Tubular Fullerenes,” J. Phys. Chem., Vol. 99, p.10694 (1995) and Saito et al., “Extrusion of Single-Wall CarbonNanotubes via Formation of Small Particles Condensed Near An EvaporationSource,” Chem. Phys. Lett., Vol. 236, p. 419 (1995). The high yield ofsingle-wall carbon nanotubes in these experiments is especiallyremarkable because the soluble fullerene yield was found to be about 10weight per cent, and much of the remaining carbon in the soot productconsisted of giant fullerenes and multi-layer fullerenes.

Example 2 Laser-Vaporization to Produce Longer Single-Wall CarbonNanotubes

In this example, a laser vaporization apparatus similar to thatdescribed by FIG. 1 was used to produce longer single-wall carbonnanotubes. The laser vaporization apparatus was modified to include atungsten wire strung across the diameter of a quartz tube mounted in anoven. The tungsten wire was placed downstream of the target so that thewire was 1 to 3 cm downstream from the downstream side of the target (13to 15 cm downstream from the surface of the target being vaporized).Argon at 500 Torr was passed through the quartz tube at a flow rateequivalent to a linear velocity in the quartz tube of about 1 cm/sec.The oven was maintained at 1200° C. and Group VIII transition metalswere combined at 1 to 3 atom % with carbon to make the target.

The pulsed laser was operated as in Example 1 for 10 to 20 minutes.Eventually, a tear drop shaped deposit formed on the tungsten wire, withportions growing to lengths of 3 to 5 mm. The deposit resembledeyelashes growing on the tungsten wire. Examination of the depositrevealed bundles of millions of single-wall carbon nanotubes.

Example 3 Two Laser Vaporization

Graphite rods were prepared as described in Example 1 using graphite,graphite cement and 1.2 atom % of a mixture of 50 atom % cobalt powderand 50 atom % nickel powder. The graphite rods were pressed into shapeand then formed into targets as described in Example 1. The graphiterods were then installed as targets in an apparatus as diagramed in FIG.2, except tungsten wire 32 was not used. A quartz tube holding thegraphite rod targets was placed in an oven heated to 1200° C. Argon gaswhich had been catalytically purified to remove water vapor and oxygenwas passed through the quartz tube at a pressure of about 500 Torr and aflow rate of about 50 sccm although flow rates in the range of about 1to 500 sccm (standard cubic centimeters per minute), preferably 10 to100 sccm are also useful for a 1 inch diameter flow tube. The firstlaser was set to deliver a 0.532 micron wavelength pulsed beam at 250 mJper pulse. The pulse rate was 10 Hz and the pulse duration was 5 to 10ns. A second laser pulse struck the target 50 ns after the end of thefirst pulse. The second laser was set to deliver a 1.064 micronwavelength pulsed beam at 300 mJ per pulse. The pulse rate was 10 Hz andthe pulse duration was 5 to 10 ns. The first laser was focused to a 5 mmdiameter spot on the target and the second laser was focused to a 7 mmdiameter gaussian spot having the same center point on the target as thespot from the first laser. About 1/10th of a second after the secondlaser hit the target, the first and second lasers fired again and thisprocess was repeated until the vaporization step was stopped.

About 30 mg/hr of the raw product from the laser vaporization of thetarget surface was collected downstream. The raw product comprised a matof randomly oriented single-wall carbon nanotubes. The raw product matis made up almost entirely of carbon fibers 10-20nm in diameter and 10to 1000 microns long.

About 2 mg of the raw product mat was sonicated in 5 ml methanol forabout 0.5 hour at room temperature. Transmission Electron Microscope(TEM) analysis of the sonicated product proved that the product wascomprised mostly of ropes of single-wall carbon nanotubes, i.e., bundlesof 10 to 1000 single-wall carbon nanotubes aligned with each other(except for occasional branching) having a reasonably constant ropediameter over the entire length of the rope. The ropes were more than100 microns long and consisting of uniform diameter single-wall carbonnanotubes. About 70 to 90 wt % of the product is in the form of ropes.The individual single-wall carbon nanotubes in the ropes all terminatewithin 100 nm of each other at the end of the rope. More than 99% of thesingle-wall carbon nanotubes appear to be continuous and free fromcarbon lattice defects over all of the length of each rope.

Example 4 Procedure for Purifying Single-Wall Nanotube Material to >99%

Material formed by the laser production method described in U.S. Ser.No. 08/687,665 was purified as follows to obtain a preparation enrichedin nanotubes. 200 mg of the raw laser-produced single-wall nanotubematerial (estimated yield of 70%) was refluxed in 2.6 M aqueous nitricacid solution for 24 hours. At 1 atm pressure the reflux temperature wasabout 1200° C. The solution was then filtered through a 5 micron poresize TEFLON filter (Millipore Type LS), and the recovered single-wallnanotubes were refluxed for a second 24 hr period in fresh nitric acidsolution (2.6 M). The solution was filtered again to recover thesingle-wall nanotube material, and the material recovered from thefiltration step was sonicated in saturated NaOH in ethanol at roomtemperature for 12 hours. The ethanolic solution was filtered to recoverthe single-wall nanotube material, and the material recovered wasneutralized by refluxing in 6M aqueous HCl for 12 hours. The nanotubematerial was recovered from the aqueous acid by filtration, and baked at850° C. in 1 atm H₂ gas (flowing at 1-10 sccm through a 1″ quartz tube)for 2 hours. The yield was 70 mg of recovered purified material.Detailed TEM, SEM and Raman spectral examination showed it to be >99%pure, with the dominant impurity being a few carbon-encapsulated Ni/Coparticles.

Example 5 Procedure for Cutting SWNT into Tubular Carbon Molecules

Bucky paper (˜100 microns thick) obtained by the filtration and bakingof purified SWNT material as described in Example 1 was exposed to a 2GEV beam of Au⁺³³ ions in the Texas A&M Superconducting CyclotronFacility for 100 minutes. The irradiated paper had 10-100 nm bulletholes on average every 100 nm along the nanotube lengths. The irradiatedpaper was refluxed in 2.6 M nitric acid for 24 hours to etch away theamorphous carbon produced by the fast ion irradiation, filtered,sonicated in ethanol/potassium hydroxide for 12 hours, refiltered, andthen baked in vacuum at 1100° C. to seal off the ends of the cutnanotubes.

The material was then dispersed in toluene while sonicating. Theresulting tubular molecules which averaged about 50-60 nm in length wereexamined via SEM and TEM.

Example 6 Assembly of a SWNT Array

About 10⁶ (10,10) nanotube molecules with lengths 50-60 nm are preparedas described above, are derivatized to have an —SH group at one end andallowed to form a SAM molecular array of SWNT molecules on a substratecoated with gold in which the tubular molecules are aligned with theirlong axis parallel and the ends of the tubes forming a planeperpendicular to the aligned axes.

Example 7 Growth of a Continuous Macroscopic Carbon Fiber

The array according to Example 6 can be used to grow a continuousmacroscopic carbon fiber in the apparatus shown in FIGS. 6 and 7. Theends of the nanotubes (which form the plane perpendicular to the axes ofthe tubes) of the array are first opened. For the 2D assembly ofnanotubes on the gold covered surface, the assembly can be made to bethe positive electrode for electrolytic etching in 0.1 M KOH solution,which will open the tips of the nanotubes.

Ni/Co metal clusters are then vacuum deposited onto the open ends of theassembled nanotubes in the SAM. Preferably, metal clusters 1 nm indiameter are arranged so that one such Ni/Co nanoparticle sits on thetop opening of every nanotube in the nanotube array.

The Ni/Co capped nanotubes in the array are heated in a vacuum up to600° C., pyrolyzing off all but the carbon nanotubes and the Ni/Coparticles. Once the pyrolysis is complete, a flow of ethylene gas isstarted, and the tubes elongate in the direction of the aligned axes toform a carbon fiber of macroscopic diameter. If a significant portion ofthe Ni/Co catalyst particles deactivate, it may be necessary toelectrochemically etch the tips open and clean the assembly again, andrepeat steps of applying the Ni/Co catalyst particles and reinitiatinggrowth of the array. A continuous fiber of about 1 micron in diameter iscontinuously recovered at room temperature on the take-up roll.

Example 8 Production of Fullerene Pipes and Capsules

Single-walled fullerene nanotubes were prepared by an apparatuscomprising a 2.5 cm by 5 cm cylindrical carbon target (with a 2 atom %of a 1:1 mixture of cobalt and nickel) that was rotated about itsprinciple axis in flowing argon (500 torr, 2 cm sec⁻¹) in a 10 cmdiameter fused silica tube heated to 1100° C. Two pulsed laser beams(ND:YAG 1064 nm, 1 J pulse⁻¹, 30 pulse s⁻¹, 40 ns delay) were focused toa 7 mm diameter spot on the side of the rotating target drum and scannedunder computer control along the length of the drum, alternating fromthe left to the right side of the drum so as to change the angle ofincidence on the target surface to avoid deep pitting. This method hasthe advantage of producing 20 grams of material in two days ofcontinuous operation.

The raw material formed by the apparatus was purified by refluxing innitric acid followed by filtration and washing in pH=10 water withTriton X-100 surfactant. The net yield of purified fullerene fibers fromthis method depends on the initial quality of the raw material, which istypically in the range of 10-20% by weight. The molecular perfection ofthe side walls, a characteristic of fullerene fibers, allows thesefibers to survive the refluxing.

The fullerene ropes were highly tangled with one other. The fullereneropes frequently occurred in fullerene toroids (“crop circles”), whichsuggests that the ropes are endless. This is due to van der Waalsadherence between the “live” ends of the ropes and the sides of otherropes during the high-yield growth process in the argon atmosphere ofthe laser/oven method. The growing rope ends were eliminated incollisions with another live rope end that was growing along the sameguiding rope from the opposite direction. In one dimension, collisionsare unavoidable.

Ends were created from the tangled, nearly endless ropes by manytechniques, ranging from cutting the ropes with a pair of scissors tobombarding the ropes with relativistic gold ions. Here, the ropes werecut by sonicating them in the presence of an oxidizing acid, such asH₂SO₄/HNO₃. The cavitation produced local damage to the tubes on thesurface of the ropes, which activated them for chemical attack by theoxidizing acid. As the acid attacked the tube, the tube was completelycut open and the tube slowly etched back, with its open end unable tore-close at the moderate temperature. Nanotubes underlying the now-cutsurface tube on the rope were exposed, and subsequent cavitation-induceddamage resulted in the cutting of the entire rope. The cut nanotubeswere subjected to further oxidizing acid treatment in order to ensurethat they are molecularly perfect and chemically clean.

The length distribution of the open-ended tubes is shortenedsystematically with exposure time to the acid. In a 3/1 concentratedsulfuric acid/nitric acid, at 70° C., the average cut nanotube wasshortened at a rate of 130 nm hr⁻¹. In a 4/1 sulfuric acid/30% aqueoushydrogen peroxide (“piranha”) mixture at 70° C. the shortening rate wasapproximately 200 nm hr⁻¹. This etching rate is sensitive to the chiralindex of the nanotubes (n,m), with all “arm chair” tubes (n=m) having adistinct chemistry from the “zig-zag” tubes (m=0), and to a lesserextent with tubes of intermediate helical angle (n≠m).

The cut fullerene tubes material formed stable colloidal suspensions inwater with the assistance of surfactants such as sodium dodecyl sulfateor a non-ionic surfactant such as Triton X-100. The suspensions wereseparated as a function of nanotube length.

AFM imaging of the cut nanotube pieces on graphite revealed that manynanotubes are individuals, but that a majority of the nanotubes were invan der Walls contact with each other. The nanotubes with lengths ofgreater than 100 nm may be closed by true hemifullerene end caps, whichform sealed fullerene capsules when annealed in a vacuum at 1000-1200°C.

Example 9 Production and Purification of Fullerene Pipes and Capsules

Referring to FIGS. 16A-C, a SEM image of raw SWNT felt material is shownin FIG. 16A, while the same material after purification is shown inFIGS. 16B-C. The abnormally low quality initial starting materialemphasizes the effectiveness of the following purification process. Theraw sample (8.5 gm) was refluxed in 1.2 l of 2.6 M nitric acid for 45hours. Upon cooling, the solution was transferred to PTFE centrifugetubes and spun at 2400 g for 2 hours. The supernatant acid was decantedoff, replaced by de-ionized water, vigorously shaken to re-suspend thesolids, followed by a second centrifuge/decant cycle. The solids werere-suspended in 1.8 l water with 20 ml Triton X-100 surfactant andadjusted to a pH of 10 with sodium hydroxide. The suspension was thentransferred to the reservoir of a tangential flow filtration system(MiniKros Lab System, Spectrum, Laguna Hills, Calif.). The filtercartridge used (M22M 600 0.1N, Spectrum) had mixed cellulose esterhollow fibers of 0.6 mm diameter, 200 nm pores and a total surface areaof 5600 cm². The buffer solution consisted of 44 l of 0.2 vol % TritonX-100 in water of which the first 34 l were made basic (pH 10) withsodium hydroxide, and the final 10 l at pH 7. The cartridge inletpressure was maintained at 6 psi. A control valve was added to the exitso that the outflow rate was restricted to 70 ml min⁻¹. The result was astable suspension of purified SWNT for which the SEM image in FIG. 16Bis typical. Filtration of this suspension produces a paper of tangledSWNT which resembles carbon paper in appearance and feel. As is evidentin the SEM image of FIG. 16C, the torn edge of this “bucky paper” showsthat the tearing process produces a substantial alignment of SWNT ropefibers. The overall yield of purified SWNT from this abnormally poorstarting material was 9% by weight.

FIG. 17 shows a taping mode AFM image of cut fullerene nanotubes (pipes)electrodeposited from a stable colloidal suspension onto highly orientedpyrolytic graphite (HOPG). The tubes had a tendency to align 120° to oneanother. They are in registry with the underlying graphite lattice. AFMmeasurements of the heights of these cut tubes revealed that roughlyhalf were single tubes 1-2 nm in diameter, whereas the rest areaggregates of several tubes in van der Waals contact. These cut tubeswere prepared in a two step process: cutting and polishing. In a typicalexample, 10 mg of the purified SWNT “bucky paper” (shown in FIG. 16B)was suspended in 40 ml of a 3:1 mixture of concentrated H₂SO₄/HNO₃ in a100 ml test tube and sonicated in a water bath (Cole Palmer model B3-R,55 kHz) for 24 hours at 35-40° C. The resultant suspension was thendiluted with 200 ml water and the larger cut SWNT tubes were caught on a100 nm pore size filter membrane (type VCTP, Millipore Corp., Bedford,Mass.), and washed with 10 mM NaOH solution. These cut tubes were thenfurther polished (chemically cleaned) by suspension in a 4:1 mixture ofconcentrated H₂SO₄:30% aqueous H₂O₂ and stirring at 70° C. for 30minutes. After filtering and washing again on a 100 nm filter, the cutnanotubes were suspended at a density of 0.1 mg/ml in water with the aidof 0.5 wt % Triton X-100 surfactant. The electrodeposition was performedby placing 20 μl of the nanotube suspension on the surface of a freshlycleaved HOPG substrate (Advanced Ceramics, Cleveland, Ohio), confiningthe droplet within a Vitron O-ring (4 mm o.d., 1.7 mm thick), cappingthe trapped suspension with a stainless steel electrode on top of theO-ring, and applying a steady voltage of 1.1V for 6 minutes. Whensuspended in water, the nanotubes are negatively charged and aretherefore driven by the electric field onto the HOPG surface. Afterdeposition the HOPG/nanotube surface was washed with methanol on aspin-coater in order to remove the water and the Triton X-100surfactant.

FIG. 18 shows the Field Flow Fractionation (FFF) of cut fullerenenanotube “pipes” in aqueous suspension. A 20 μl sample of 0.07 mg/mg cutnanotube suspension in 0.5% aqueous Triton X-100 was injected into across-flow FFF instrument (Model F-1000-FO, FFFractionation, LLC, SaltLake City, Utah) operating with 0.007% Triton X-100 in water mobilephase at 2 ml min⁻¹, and a cross-flow rat of 0.5 ml min⁻¹. The solidcurve (left vertical axis) of FIG. 18A shows the light scatteringturbidity (at 632.8 nm wavelength) of the eluting nanotubes as afunction of total eluent volume since ejection. The open circles (rightaxis) plot the estimate radius of gyration of the nanotubes as measuredby a 16 angle light scattering instrument (DAWN DSP, Wyatt Technology,Santa Barbara, Calif.). FIGS. 18B, 18C, and 18D show nanotube lengthdistributions from FFF eluent fractions 1, 3, and 5, respectively, asmeasured from AFM images of the suspended fullerene nanotubeselectrodeposited on HOPG as in FIG. 17.

FIG. 19 shows an AFM image of a fullerene nanotube “pipe” tethered totwo 10 nm gold spheres, one at either end. The tube was electrodepositedonto HOPG graphite from a suspension of a mixture of such tubes withcolloidal gold particles (Sigma Chemical Co.) in water. The irregularlyshaped features in the image are due to residual deposits of the TritonX-100 surfactant used to stabilize the suspension. The nanotube-to-goldtethers were constructed of alkyl thiol chains covalently attached tothe open ends of the tubes. Presuming these open ends were terminatedwith many carboxylic acid groups as a result of the acid etching inprevious processing, they were converted to the corresponding acidchloride by reacting them with SOCl₂. These derivitized tubes were thenexposed to NH₂—(CH₂)₁₆—SH in toluene to form the desired tethers, withthe thiol group providing a strong covalent bonding site for a goldparticle. Most tubes derivitized this way have a single gold particlebound to at least one of their ends, as revealed by extensive AFMimaging.

Example 10 Composite Material Containing Carbon Nanotubes

One gram of purified single walled fullerene nanotubes is dispersed in 1liter of dichloro-ethane, together with 10 grams of Epon epoxy. Thehardener is added to the solvent removed by vacuum rotary evaporation.The resultant fullerene nanotube-epoxy composite is then cured at 100°C. for 24 hours.

Alternatively, a carbon fiber, fullerene nanotube composite can beprepared by drawing one or more continuous carbon fibers or woven carbonfiber tapes through a vat containing the above dichloroethane epoxynanotube suspension, and then winding this impregnated tape around adesired form. After curing in an autoclave in a fashion known in thecarbon fiber-epoxy composite industry (see, e.g., D. L. Chung, CarbonFiber Composites (1994)), a composite of superior delaminationresistance is produced. The fullerene nanotubes within the compositestrengthen the epoxy between the carbon fiber layers. A superiorcomposite is produced if one uses fullerene fibers for both the woventape layers and the tangled nanotube strengtheners within the epoxyphase.

Modification and variations of the methods, apparatus, compositions andarticles of manufacture described herein will be obvious to thoseskilled in the art from the foregoing detailed description. Suchmodifications and variations are intended to come with the scope of theappended claims.

1. A method for purifying a mixture comprising single-wall carbon nanotubes and amorphous carbon contaminate, said method comprising the steps of: (a) heating said mixture under oxidizing conditions sufficient to remove the said amorphous carbon; and (b) recovering a product comprising at least about 80% by weight of single-wall carbon nanotubes, wherein the product is washed with a solution comprising a surfactant.
 2. The method of claim 1 wherein the surfactant is sodium dodecyl sulfate.
 3. The method of claim 1 wherein the surfactant is a non-ionic surfactant.
 4. A method for purifying a mixture comprising single-wall carbon nanotubes and amorphous carbon contaminate, said method comprising the steps of: (a) heating said mixture under oxidizing conditions sufficient to remove the said amorphous carbon; and (b) recovering a product comprising at least about 80% by weight of single-wall carbon nanotubes.
 5. The method of claim 4 wherein said oxidizing conditions comprise an aqueous solution of an inorganic oxidant.
 6. The method of claim 5 wherein said inorganic oxidant is selected from the group consisting of nitric acid, a mixture of sulfuric acid and hydrogen peroxide, potassium permanganate and mixtures thereof.
 7. The method of claim 5 wherein said aqueous solution is heated to reflux.
 8. The method of claim 5 additionally comprising the step of subjecting the oxidized product of step (b) to a saponification treatment.
 9. The method of claim 8 wherein said saponification treatment comprises contacting said product with a basic solution.
 10. The method of a claim 9 wherein said basic solution comprises sodium hydroxide.
 11. The method of claim 9 additionally comprising the step of neutralizing the saponified product with an acid.
 12. The method of claim 11 wherein said acid is hydrochloric acid.
 13. The method of claim 11 additionally comprising the step of recovering a solid product from the saponified, neutralized product.
 14. The method of claim 13 wherein said product is recovered by a method selected from the group consisting of filtration, settling by gravity, chemical flocculators, and liquid cycloning.
 15. The method of claim 13 wherein said solid product is a paper-like two-dimensional product.
 16. The method of claim 15 additionally comprising the step of drying the product.
 17. The method of claim 16 wherein said product is dried at about 850° C. in a hydrogen gas atmosphere.
 18. The method of claim 4 wherein said product comprises at least about 90% by weight of single-wall carbon nanotubes.
 19. The method of claim 4 wherein said product comprises at least about 95% by weight of single-wall carbon nanotubes.
 20. The method of claim 4 wherein said product comprises at least about 99% by weight of single-wall carbon nanotubes.
 21. A method for purifying a mixture comprising single-wall carbon nanotubes and amorphous carbon contaminate, said method comprising the steps of: (a) heating said mixture under oxidizing conditions; and (b) recovering a product comprising at least about 80% by weight of single-wall carbon nanotubes, wherein the product comprises fullerene torroids. 